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New LiFePO4 Lithium
House Bank
Battery Charging
System Philosophy
Trickle Charging
Start Battery
Solar Charging System
Alternator Repair Lightning Issues
LiFePO4 Reference Sources

Last Updated: 10/06/2021

The electrical systems and issues on our previous boat, a 1980's CSY monohull, were quite different than those on our 2004 St. Francis Catamaran.  For all the great stuff I did over the years on the CSY electrical system, go to this link:  CSY Electrical Systems.

Future Additions:
Alternator-Regulator Engine Charging

Lithium LifePO4 Battery Upgrade

About a year ago (2020), after much careful study, we embarked on replacing our 13 year old Gel batteries with lithium LiFePO4 cells. In doing so, we quickly learned the following:

  • The technology and supporting equipment are still evolving, with a multitude of choices available
  • No serious cruiser should change from lead acid to lithium batteries unless they are willing to spend a substantial amount of time in research and effort and money for a proper installation.
  • There are many opinions regarding how best to do this; even the experts’ opinions differ. But there are several trusted information sources. See the list at the end of this article, here.
  • Competition among sellers of lithium equipment is stiff, especially among cell and Battery Management System (BMS) producers.
  • Not everything you read on seller websites is true, and some important things that are not there are true, and the more specifications, the better.
  • In order to create a successful installation you must have an open mind and be curious about what others have done, and be involved in all of the installation work.

Our installation is optimized for a catamaran cruising full time overseas. We have little tolerance for jury rigs, marginally safe practices and unnecessarily high cost equipment. We believe that if installing lithium on a boat, it is necessary to develop the skills to make repairs ourselves with adequate spares and proper tools.

After significant research, money expended, and living with the new technology for about 6 months, below find our thoughts on how to complete a DIY LiFePO4 lithium cell installation on a cruising sailboat. This may differ significantly from an installation for an off-grid home, an electric vehicle and even a power boat used for coastal cruising.

When we purchased our St. Francis 44 catamaran 6 years ago, the house bank consisted of six 6-volt Sonneschein Solar Block 200 batteries, for a total of 600Ah. They are very high quality German Gel batteries. In early 2020, locked down by COVID, and with our gel battery bank now 13 years old, we decided it was a good opportunity to upgrade to new Lithium technology. The Gels might have lasted several more years according to Gel literature, but given our location in SE Asia, and the time we had available, this was a good opportunity to upgrade.

Had we not had the years’ time to study the technology, place the orders, and make the many necessary electrical system changes, we would not have taken this on. It is not a project for those not willing to spend time learning how to do the installation properly.

Lead Acid (LA) vs Lithium (LFP) Differences: Because of the vast differences between these two types of batteries, great care must be taken to not make a mistake during planning and installation. A number of different lithium type cells are available now, but LiFePO4 is the best choice for cruiser batteries. Below are some differences between LiFePO4 and LA technologies:

  • They do not require a full charge on a daily basis; in fact, charging to only 90%, or even less, will give a somewhat longer service life.
  • With LFP, no absorption or float charging is needed, only bulk.
  • 80-90% of LiFePO4 capacity is useable on a regular basis vs a maximum of 50% for lead acid under ideal conditions.
  • Cell level monitoring, balancing and disconnect control are required with LiFePO4, whereas only total battery voltage is typically monitored for charging with LA.
  • There may be some significant electrical system modifications required for a proper lithium installation.  These include purchase of a reliable battery management system (BMS), installing separate charge and load busses and using separate inverters and chargers.
  • Charging with an alternator requires some modifications, or you risk burning your alternator internals.  You must either make sure the alternator is externally regulated by a smart alternator regulator with alternator temperature control, or use battery-to-battery charging, possibly with a lead acid battery connected to the alternator.
  • Finally, long term storage requires placing LiFePO4 cells at about 50% state of charge (SOC) and in a relatively cool location for best longevity.

LifePO4 Cells:  After a great deal of research, we settled on prismatic style aluminum cased LifePO4 cells, purchased directly from RJ Lithium in China. There are a number of other Chinese cell companies we could have bought from, but other cruising friends locally had researched this and were buying from RJ. Their reputation was good, they offered documented Grade-A cells, the sales representatives were responsive, the website was informative, and they offered a 5 year warranty.

Our 8 Cells

All eight of our cells with taped terminals just out of the shipping boxes

One bank of 4 cells

Four of our prismatic cells with grade A testing stickers intact

We purchased eight 3.2 volt 271 Ah LifePO4 cells, for about $150 each plus about $35 shipping each for a total house bank capacity of 540 Ah. (Note that the shipping cost was excessively high due to the peculiarities of shipping into the Philippines via Hong Kong).

Of that 542 Ah, about 450 Ah are useable, so we increased our capacity by about 50% over our Gel battery bank's useful capacity. And we were able to remove 390 lbs of Gels and replace with only 100 lbs of lithium cells.

Later we discovered that we could have bought similar well-regarded EVE or Lishen cells for $100 each and modest shipping cost, sourced locally here in the Philippines, but without the longer warranty.  So our cost for the RJ cells was about $1500 US including shipping.  Lishen or Eve cells would have been around $900 including shipping. The LFP cell market is constantly changing, and competition is fierce, so this pricing may no longer valid.

Drop-In LifePO4 Batteries: We do not recommend installing what is commonly referred to as ‘drop in lithium batteries’ on a serious cruising boat. They are better suited to coastal power boats and outboards for the following reasons:

  • The cells and BMS are often secured inside a sealed battery box and may be inaccessible if there is a problem. 
  • Typically, the BMS provided is SE Asian and uses small internal Mosfet relay components that must control the high currents usually found on cruising boats.  If anything goes wrong the owner may have to replace the entire battery and BMS.
  • There may be little adjustment available to the charging and other control parameters which you may want to customize for your installation and longer service life.
  • They can be frightfully expensive compared to a DIY installation using individual cells and separate BMS.
  • You will still need to do many of the same modifications to your electrical system as with a DIY system.

If you can’t take the time to do a proper DIY installation yourself, or with help from a knowledgeable friend who will teach you the system, we recommend buying quality Gel batteries to install into your existing electrical system.

Cell Matching and Balance: Factory matching of cell capacity and internal resistance is important to being able to maintain cell voltage balance. But it is a labor intensive, and therefore expensive, process. The cell charging curve is very flat in the middle between 3.20-3.4v per cell. Then it goes nearly vertical (the knee) as the cell approaches full state of charge (SOC) at about 3.45v per cell and above. Likewise, as the battery is discharging, the voltage stays very flat until dropping off rapidly below about 3.15vpc as the battery reaches 10-15% state of charge.

Charge Curve for 4 Cells in Paralell

Charge Curve for 4 Cells in Parallel
Charging at 50 amps for 18hrs and 40 minutes
(small downward spikes are when we paused charging for the day)
Note vertical voltage rise at approx 3.5v (14.0v in a 12v system)

LifePO4 Cell Discharge Curve

This curve reflects one cell being discharged from "full" at 35 amps continuously.
Of note is the flat curve until the cell reaches 3.15, and the rapid drop-off after that.

If the cells are not perfectly matched in capacity and internal resistance, when charging one cell can get to 3.65 volts per cell (vpc), well before the others, when charging. This is an over voltage situation that can destroy that cell before the total battery voltage reaches an alarm condition. Likewise, when discharging, if one cell is slightly more depleted than the others, its voltage can drop rapidly to below 2.5vpc, a destructive under voltage situation, again while the overall battery voltage is still at a safe level.

Also, cells that are not well matched will have slightly different charge curves that might cause an automatic balancer to balance the wrong cells during charging. Our cells are not perfectly matched, so their charge curves intertwine voltage levels as they are being charged.  Sometimes the low voltage cell at the start of charging becomes the high voltage cell at charge termination. A good cell balancer can handle this and keep cell balance levels within a reasonable delta.

Well-regarded lithium factories produce thousands of individual cells a week. During initial testing, those that match advertised specifications are graded as A cells. Those that do not become grade B cells and could have a range of problems.  Both are sold on the open market. Grade A cells are usually a bit more expensive, have QR and testing stickers intact and usually have warranties. Grade B cells are often sold to off grid applications that use hundreds of cells so that they can afford to have a few that have problems. Serious cruisers would do well to always buy Grade A cells as it ensures full bank capacity and makes balancing much easier.

Even after being assured we had grade A cells, and doing exhaustive testing upon receipt, we ended up with one bad cell that would excessively self-discharge compared to the others.  It lost a half millivolt (mv) at rest on a daily basis, which resulted in it quickly falling behind the others at charge termination.  This is one symptom of a grade B cell.  After much testing and consultation with RJ to discover the source (swapping cells around, etc), we determined it to be an internal problem.  To their credit, RJ replaced the cell under warranty with us paying the $20 US shipping cost.  Meanwhile, we had purchased two grade B similar cells from a Lishen internet store in Manila.  They have performed well so far, but we will eventually go back to using all RJ cells in our house bank.  The Lishen cells will become spares. And as we all know, cruisers can never have too many spares.

Configuration: Banks of lithium cells are typically wired in sets of four 3.2 volt cells in series for a nominal 12 volt battery system. If you have a 24 volt electrical system, wire 8 cells in series. For more capacity than 4 or 8 single cells will allow, first wire cells in equal parallel sets, then those sets wire in series.

We originally planned to configure our 8 cells cells into two 4-cell "batteries", with a 1-2-Both selector switch so we could switch between batteries if we ran into a problem with one battery.  However, once we started wiring up the two required BMS's, we found that trying to control the separate loads, charging sources, and 2 busses with two BMS's got too difficult. We also found that rearranging the cells from an 8-cell single bank to a 4-cell bank, if we ran into a very rare sudden cell problem, to be pretty simple.

So we ended up with 4 sets of 2 cells in parallel to make 4 "supercells", then those 4 cells in series for a 542Ah at 13.2v bank. This also had the advantage of requiring only one BMS instead of two. Since we had ordered two BMSs we now had a spare.  And as all cruisers know...

Whether our configuration is called 2P4S or 4S2P configuration depends on who you ask. It is written both ways all over lithium literature and the internet. So be mindful of this when asking questions on lithium forums.

Cell Compression: Most literature and experts on LFP cells recommend using a ‘compression box’ to house the cells. This is more of a 'limitation box' that prevents the cells from chafing against each other, terminals being damaged by connector tension as a result of expansion during charging, and sliding around as a bank in rough weather. Also, according to EVE Energy, one of the largest lithium cell manufacturers in China, their aluminum case cells require compression in order to reach their full service life. Many others agree.

So we built a compression box to store the cells using epoxy coated ¾” marine plywood and 3/8” SS threaded rod. Between the cells we used 1mm Formica to prevent the cell sides from shorting together. The box is strongly secured, has a polycarbonate cover, and is mounted under our main cabin settee only about 3 feet from the BMS and busses. The addition of calibrated springs on the threaded rod would allow us to control the amount of compression.

Our Battery "Compression Box"

Our 8 LifePO4 cells in their compression box in a 2P4S configuration.
RJ provided quality cell terminal connecting straps which are made of multiple layers of flexible copper. With some research, aluminum straps could also be used. All connections should be firmly fastened to the terminals.

Battery Box, Closed Up

Front of our Battery Box, cover on and secured.
Red cable is positive and brown negative.
Small gray wire is solar MPPT sense.

Battery Management System (BMS):  A good BMS is a critical component of a LifePO4 system. Unlike most lead acid battery monitors that display overall battery voltages, a good BMS should monitor individual cell voltages. So a BMS can watch the voltage and state of charge of each cell, and make appropriate decisions regarding when to disconnect charge sources in case of an over voltage event (HVD) or disconnect loads in case of an under voltage event (LVD) in order to prevent cell damage.

There are two types of BMSs. One uses small internal MOSFET relays to turn on and off charging and loads when required.  The other type of BMS can control much larger external relays. Since loads like inverters and windlasses and charging sources like alternators and generators might involve relatively high currents, cruising boat systems are better done with a BMS that uses high capacity external relays.

An important BMS feature is its ability to display what it is doing and important battery details such as voltage, current and SOC. Options include hard wiring to a display device such as a computer, wireless Wifi, and wireles Bluetooth using an application. We are using Wifi so that we can see what is happening with our system when on or off the boat.

Also, a good BMS will have some sort of cell balancing capability. A couple hundred milliamps are sufficient to keep most reasonably matched and balanced cells in line. Although most BMSs use some form of low current passive balancing, and that is usually sufficient, larger active balancers that remove excess Amp Hours from high voltage cells and place it in lower cells are commonly available. This just reduces the time it takes to balance wayward cells with the others.

BMSs range in price from inexpensive/dumb $15 USD small open boards with no user interface, to high-quality programmable BMSs that will integrate seamlessly with existing proprietary equipment like smart Victron components for about $600 USD.  Price doesn’t always give you the best equipment with features you may want, but better BMSs are priced over $100 US.  There are many internet sources for comparing BMSs.  But remember serious cruisers cannot afford unreliable gear, so paying for quality and reliability is worthwhile.

We chose a very smart programmable BMS, an Electrodacus SBMS0, made in Canada by a small well-regarded company. This one is targeted at the DIY Solar community and can control multiple external relays with many adjustable parameters. It has an included detailed monitor screen, a small balancer,  excellent HVD/LVD protection capability, and an optional Wi-Fi interface. Just about every parameter for charging, discharging, balancing and HVD/LVD control is adjustable by the user.  The HVD/LVD controls have 6 ways to set the control function.

Our Electrodacus Monitoring Screen

The SBMS0 Main Monitoring Screen, one of about two dozen screens available for monitoring and parameter adjustment.

The Electrodacus SBMS0 also has some built-in historical logging, and with the addition of the optional Wi-Fi module, can provide a wireless MQTT feed to integrate into any Internet-of-Things (IOT) system.  The MQTT capability allowed us to build a custom monitoring and logging screen (below), running on our Nav Station Computer. With internet access, and a bit of free software, we can monitor our electrical system from anywhere in the world.

Our Custom Charge Monitoring Screen

 Our Battery Management monitoring screen, using the MQTT feed
from the Electrodacus, and built using Mosquitto and Node-Red.
This is under constant revision by our onboard IT person.
(More about this)

We are pleased with our choice of BMS, but it has involved a steep learning curve. (LifePO4 in general is a big learning curve!)  Considerable help is available from the detailed User Manual, an even more helpful user built Beginners’ Guide, two forums with experienced users and the developer, Dacian, answering questions.  Plus multiple articles and YouTube videos by various users.  Dacian will even diagnose problems and fix them if necessary, sometimes at no charge, if you send the unit to him.

And then there is the detailed information about our installation on the Electrodacus page on our website.

Wiring & Fuses: It is important to use proper wire sizes, quality terminals, and make good connections, because proper monitoring and balancing involve millivolts and milliamps (thousanths of volts and amps). Any weak connection will affect readings and function.

The display and balancing wires are typically 20 gauge or smaller, so you might need better crimping and stripping tools. For example, the ElectroDacus system uses twisted solid Cat 5 or 6 24 gauge wires for connections to the SBMS0. Common stripping tools won’t strip those small wires. (See our tool recommendations below).

Fusing and circuit breakers must be of quality construction and function as advertised.  These relatively small batteries can produce huge amounts of amps if shorted. Although fires are rare with LiFePO4 technology, a shorted cell can melt tools instantly and cause sparking that can ruin your day and your boat.  Proper installation will also prevent disapproval of an insurance claim should something go wrong. It is worth checking your insurance information to see if there are any specific clauses about LFP batteries.

Relays & Shunts: When using a BMS capable of controlling external relays, care must be taken regarding which relays to use for which circuits. And quality shunts must be used in order to display accurate current flow and State of Charge (SOC). Below is a list of those we used:

  • Solar charging: In case a High Voltage Disconnect (HVD) event occurs, we used two of the ElectroDacus DSSR20 relays for the SBMS0 BMS to disconnect the four 200 watt panels from the Morningstar Tristar-60 MPPT solar controller. The DSSR 20 relays can each handle up to 20 amps of current, so are perfect for our 800 watts of 24v solar panels. For now, the MPPT handles the daily charging and charge termination based on total battery voltage of 13.8v (3.45vpc).  Our MPPT has a battery sense wire, so has a very accurate measure of battery voltage (not all MPPT's have battery sense wires).

    The SBMS0 cuts off charging (via the DSSR20's) in case of a high cell voltage event at 3.55 vpc.  The SBMS0 could handle both cutoffs, but we need the MPPT controller in this circuit anyway since it handles the voltage conversion from the 24v 72 cell panels to the boat’s 12v electrical system.  And the MPPT gives us an extra layer of independent disconnects.

    If the panel voltage matched the boat’s voltage there would be no need for the expensive solar controller, and the BMS could handle charge termination without any solar controller (one of the unique features of the Electrodacus design).

  • Shore Power Charging: We have a Sterling Power Pro 60 Amp AC charger, which we bought specifically because it has a "LifePO4" charge profile.  Unfortunately, that charge profile is unrealistic for LiFePO4 cells.  The minimum absorb setting is 60 minutes, and cannot be changed. So if it is controlling the charging it will have to be manually shut off when the battery reaches charge termination, as the experts recommend little or no absorb time for LFP batteries.

    However, cutting off charging can be controlled by the BMS using a Fotek 40 amp AC-DC solid state relay (SSR) placed in the AC load wire between shore and the charger. This allows the BMS to control the charge termination of a high voltage event by disconnecting the AC, not the DC wiring.  We rarely use shore power for charging, even at the dock, so for now we are just disconnecting the unit from the batteries using a large circuit breaker in the DC wiring.

  •  Alternator Charging: We have two small 60 amp externally regulated alternators, one on each engine. Our Very Smart Regulators (VSR) can be easily configured to handle LiFePO4 charging with both time and tail current regulation and temperature and voltage sensors. (Our VSR's are the predecessor to the popular Wakespeed 500 Smart Alternator Regulator). They also have an output throttle which we have set to curtail amps out to 75% of maximum possible.

    The SBMS0 controls the alternator HVD by disconnecting the ignition/enable wire from the regulator using 10 amp Fotek DC-DC solid state relays (SSRs). This is preferable to disconnecting the alternator field wire from the regulator because it safely turns off both the alternator and regulator.  Since we don’t normally use the alternators for charging, we also have a simple on off switch in the ignition wire so charging can be shut down when the engine is running. We are still refining this system.

  • Switches and Resistors: Most of these relays are a little larger than a matchbox and use about 5 milliamps or less when energized. Because we rarely need to use the AC charger or alternators, we also have small on-off switches in their control circuits from the BMS to turn the relays off when not in use. These relays require a small resistor in the circuit to prevent excess current getting to the SBMS0 in case of a short.
  • Buss Disconnects: As a second line of defense in case of over/under voltage problems, the SBMS0 also controls two high capacity Victron Battery Protect relays. These are placed between the shunts and busses. They can to separately disconnect the entire charge or load busses from the battery in case of a problem that wasn’t handled by the charging sources or other relays. Their HVD/LVD voltages are set at cell voltage maximum/minimums of 3.65 and 2.50 vpc.
  • Shunts: In order to be able to sense current and calculate SOC shunts are required. If one is used for the battery and one for the charging sources, charge, battery, and load currents can all be displayed. In the ElectroDacus system, both shunts are mounted on the positive battery cable. We used quality 100 amp 100 mV shunts from Reidon properly sized for our equipment.

Initial Testing and Balancing: Not everyone will have the time or want to do the initial testing that we did. We had purchased the cells with an electrical engineer friend--a total of 24 prismatic 271 Ah cells.  Our friend had the proper large load and bench power supply equipment available, and we wanted to fully test that the capacity of the cells we received matched the manufacturer specs. This may be the only way to discover early on a cell lacking capacity or with a high internal resistance.

We started by charging all cells up individually to 3.6 volts per cell (vpc). Then we discharged them individually to 2.8 vpc and graphed the resulting discharge curve and capacity. Finally, we made a graph of the charge curves taking them back up to 3.6 vpc.  (see graphs earlier)

 After removing the charge, each cell fell back to a rest voltage of about 3.35 vpc. All capacities were within a few amp hours just below 271, since we did not fully charge or discharge them. The charge and discharge curves were similar, but not exactly the same. Internal resistance for all cells was measured to be .076 ohm at 3.0 vpc.

Top Balancing:  Later we did what is referred to in the literature as a ‘top balance’. That is taking all cells in parallel to some voltage above 3.5 vpc--in our case to 3.62 vpc--and letting them absorb to about 5 amp or less tail current. This should get them all balanced to within a few millivolts of each other at charge termination.

Although we did this a second time to less than 1 amp tail current, we did not find it to be very effective at getting the cells closer than about 100 mv apart at charge termination of 3.45 vpc. It probably would have been better to take them only to our charge termination voltage and let them absorb there to an absolute minimum tail current.  There are a number of opinions on the internet as to exactly how best to do this.

We found the most effective balancing technique to be using our bench power supply and adjustable load equipment to manually get the cell voltages closer at charge termination. This consists of attaching the equipment to individual or a group of cells to raise or lower their voltage by adding or subtracting milliamps over time.

Regardless of how the cell voltages look at rest, they will always have a much higher delta when the voltage reaches the knee. After a week or so of adding and subtracting mA, cell voltage deltas can be reduced to an acceptable 10-20 mV.

Then the small passive automatic balancer in the SBMS0 can be used to keep them in balance, despite our not-well-matched cells.

The balancing mechanism on our BMS uses resistors that are latched in during charging, when the cell voltage delta goes above the minimum balancing setpoint, to suppress charging the highest cell(s). So the lowest cells receive full charge current, while the highest cell(s) receive less.

Our cells are now resting with a 7 mV delta and 20-30 mV delta at charge termination. These figures are entirely adequate for cell balance.

Tools and Equipment: We purchased the following equipment to help us better do the installation:

• Long Wei PS1310F DC bench power supply. [Amazon Link]
• 20 amp 180 watt adjustable load  [Amazon Link]
• ISDT BattGo BG-8S 2 ea monitor balancer  [Amazon Link]
   (used for cell voltage monitoring prior to receiving ElectroDacus)
• UNI-T UT-61E very accurate multimeter with logging  [Amazon Link]
• UNi-T UT-210E clamp multimeter  [Amazon Link]
• Titan 11477 ratcheting terminal crimper, yellow and black handles  [Amazon Link]
• Klein Katapult 11063W wire stripper  [Amazon Link]
• Klein 11074 blade for 16-26 ga (Cat 6) wire  [Amazon Link]
• Manual large terminal crimper for #8 to 2/0 terminals
• Various wire terminals from 2/0 to 24 ga, heat shrink tubing, Cat 6 cable
• Assortment of 1 watt resistors
• Fotek AC-DC 40 amp SSR w/ cover and heat sink  [Amazon Link]  [Heat Sinks]
• Fotek DC-DC 10 amp SSR -3 each with clear plastic covers and heat sinks
• Reidon 100 amp 100 mv shunts- 2 each  [Reidon]  [Amazon Equivalent]
• Victron BP-100 Battery Protect (100 amp for charge side) [PKYS]
• Victron BP-220 Battery Protect (220 amp for load side) [PKYS]
• ElectroDacus SBMS0 BMS with Wifi  [Electrodacus]
• ElectroDacus DSSR20 relays- 2 each  [Electrodacus]
• RJ 271 Ah prismatic aluminum case cells- 8 each  [RJ Lithium]
• Also spares: We have spare cells, a spare BMS, spare DSSR20's, and spare SSR's.

Electrodacus and Control Wires
The ElectroDacus SBMS0 with polycarbonate cover and control wiring
mounted near Nav Station
Alternator Regulators and Solid State Relays
Smart alternator regulators and
solid state selays (for HVD)
Solid State Relays to Cut off Solar Panels
2 ElectroDacus DSSR20 Solid State Relays to Provide High Voltage Disconnect for Solar Panels
Solid State Relay to Cut off AC Charger
Solid State Relay for HVD for AC Charger
Victron Battery Protect BP-100
Victron Battery Protect for Controlling Busses

Lithium Safety and The Insurance Issue

• LifePO4 technology is different from, and safer than, Lithium batteries used in electronic devices like cell phones, and those in cars.
• As mentioned several times above, cruisers installing lithium, whether themselves or using an installer, should first become as familiar with the technology as possible. For us that meant months of research on line using the trusted references in our article.
• Quality of equipment is a big problem not only with lithium batteries but with all equipment used on a boat. The competition for lithium battery market share is fierce and all sorts of claims are being made by unscrupulous dealers.
• The danger from a cell problem is minimal, but danger from a poor installation or equipment is significant. So a cruiser must intimately be involved in both.
• There are several ways to do a lithium installation, including for off grid homes and electric vehicles where a failure is not such a big problem. Not all are suitable for a cruising boat, especially one travelling overseas, where failed equipment or poor installation techniques can spell disaster.
• I suspect that most underwriters are suspicious of Chinese lithium batteries and BMSs (where almost all of these are made). However, even most ‘US’ branded ‘drop in’ lithium batteries use Chinese cells and BMSs. We used grade A Chinese prismatic cells and a separate Canadian BMS, both of high quality and unlikely to fail. But we still carry spares.
• Not all installers, though ‘certified’, will be as familiar as you might like with your marine installation. If using an installer, you must be familiar with your boat’s electrical system and what will be required for a ‘best practices’ installation. Make sure the installer is also, and you both agree with the installation details, especially the equipment.
• Watch the installation very closely and double check the installer’s wiring and terminations. This will further familiarize you with the system and hopefully allow you to effectively troubleshoot a problem in the future.
• If you have done the research, know what you are doing, and are willing to do the installation yourself, you can save a considerable amount of money and ensure a proper installation. It is not rocket science. If we can do it properly, so can you.
• A lithium battery installation is not for everyone. If lithium installation challenges are insurmountable, our experience with high quality Gel batteries has convinced us that they are the best lead acid technology for cruisers.

And a couple of thoughts on insurance coverage:

• Insurance coverage is all based on risk. Underwriters want to reduce their risk to match the premium charged. There is a lot of risk insuring US boats including legal challenges, tropical cyclones, inept owners, and now faulty lithium battery installations.
• Insurers are much more careful now than before. Getting any marine insurance has become significantly more difficult. Boat location and age and owner qualifications, experience and claims history all matter now.
• Weather related losses in the Carib and US have been high over the past few years due to huge numbers of boats left in marinas, yards and mooring fields during exceptionally strong hurricanes.
• One possibility for a cruiser installing lithium might be to negotiate with the underwriter exempting losses from a lithium battery problem. If successful, that would present the opportunity do your own work and personally ensure a proper marine installation.
• Finally, a cruiser might delay a lithium installation until leaving for overseas where insurance coverage might be easier to obtain. For us, SE Asia during Covid was a great place and time to do the installation ourselves.

LiFePO4 Reference Sources

Have fun learning about this new technology, but remember that not everything you read is true, and the experts don’t all agree.  The forums, especially, are full of inaccurate opinions.  So study carefully, and subscribe as we did, to the preponderance of evidence from the trusted sources below.

A good way to start is to watch some of Will Prouse’s YouTube videos, then graduate to some of those from Andy’s Off Grid Garage, and finally read the detailed articles at MarineHowTo and NordkynDesign. Once finished you will be ready to start your LFP project. Links to these resources below.

YouTube Videos

Will Prowse's DIY Lithium and Solar on YouTube [link]

Andy's Off Grid Garage [link]

Bussed_As NZ's DIY Lithium and Solar on YouTube [link]

Articles's LifePO4 on a Boat
This is an excellent beginner's guide.'s Lithium Pages
This is a much more detailed and technical discussion, divided into seven segments, recently updated.

Stan Honey's Thoughts on LifePO4 Batteries on Boats (PDF)  [link] or [alt link]

An excellent summary of BMS features is provided in this document on DIY Solar:

Beginner's Summary of BMS Functions, Types, and Features

More DIY Solar Forum "Beginner's Resources"  [link]

ElectroDacus-Specific Information

We have consolidated our knowledge and experience (with contributions from others) for the ElectroDacus SBMS0 BMS on a separate ElectroDacus page.


Battery Charging System Philosophy

This is a big subject and it is always interesting to see how others are set up also. Much of how you set up the boat depends on how you plan to use it. If you are dockside most of the time you will want a different system than if you are cruising and away from docks. We are currently cruising, often away from docks and also away from good (expensive) repair facilities.

It has taken me several years to get my new catamaran set up the way I wanted it... with all charging systems wired to the House bank and a trickle charge arrangement for the Start battery.  On the catamaran it is a little more complicated because we now have 2 engines and 2 alternators to worry about.

My system keeps the House and Start batteries physically isolated from each other in the normal use/charging situation. It allows multi step charging for the house bank and trickle charging for the start battery.

First, connect all your charging sources (alternator, 120v charger, solar, etc) on one "charge bus" and connect that directly to the house bank.

Run your charging sense and temperature wires to the house bank.

Connect your starting battery direct to the starter. Then connect the house bank to terminal 1 of the battery selector switch and the start battery to terminal 2.

Next connect all your loads to the common terminal of your battery selector switch. Add cutout switches and/or fuses as desired in the battery cables within 18" of the batteries, if you want to comply with ABYC specs.

Finally, connect the positive posts of the house and starting batteries together with 12 ga wire and a thermal circuit breaker and diode.

See Trickle Charging the Start Battery, for details, below.

So, if you leave the battery selector switch on 1--the normal situation--the starting battery starts the engine, and the house bank runs all the loads. And the two batteries/banks are isolated. If the start battery fails, you can temporarily place the switch on Both to combine them for starting.

Also, keep your house batteries away from heat while charging, as it is a killer. If in the engine room, for example, with temps over 115 degrees F you will lose 75% of your cycle life! And if you are using Lead Acid technology for your house bank, don't forget to equalize!


Start Battery Trickle Charging

At the 1998 SSCA Gam the Four Winds/Everfair owner, Bill Owra, gave what I thought was a very well thought out and much better wiring diagram for a house bank and a starting battery setup.  It featured, among other things, hands off trickle charging of the start battery off the house bank, an anti theft switch in the starter/starter battery cable,  using the battery selector switch to normally control only battery loads, rather than charging and loading, emergency cross connect for starting and house loads, and routing all charging source cables directly to the house bank so there’s no possibility of an alternator or other disconnect problem while charging.  It was the best layout I've seen and I've looked at many in the past 20 years of boat ownership.

I thought that the best feature was the automatic trickle charging of the starting battery from the house bank through a short 12 gauge wire with a diode (one way current flow) and thermal circuit breaker. 

The idea is that when the house bank is being charged from any charging source the diode will keep the voltage to the starting battery about 1/2 volt below the house bank voltage, and the thermal circuit breaker will break the charging circuit off if the charging amperage get too high. 

The starting battery can take up to about 15 amps if it needs it but with this system it normally just takes small float current.  I've never seen more than about 2 amps going into my starting battery from the house bank.

Battery Charging System Wiring 

This circuit provides a reasonable float charge to keep the starting battery always at 100 percent, just like in your car.  A true starting battery with thin, large surface area plates and a high CCA/MCA rating is great for starting your engine and will last as long as your house bank if kept this way. 

And it's all automatic with no risk of inadvertently disconnecting the house bank from its alternator charging source.  I also keep a couple of spare diodes and thermal circuit breakers aboard just in case.

I used this electrical layout on our CSY, and have just (2018) installed it on our new catamaran.  Here are the components required:

Thermal Circuit Breaker and Schotke Diode

And links to online sources:

20amp Thermal Circuit Breaker

60amp 35v Schottky Diode (MBR6035)

And a picture of ours, installed.  I just mounted it on a piece of scrap aluminum, near the battery box:

TCB and Diode Installed


Solar Charging System

For the evolution of our solar system on Soggy Paws the CSY, see this page.
CSY Solar Charging Evolution

When we bought the catamaran, I sold off the old system that came with the boat and installed 4 new 200 watt 36v panels, and a new Morningstar MPPT solar regulator.  Though we really liked the Outback MPPT regulator that we had on the CSY, the Morningstar offered a way to monitor the system via computer connection.

Soggy Paws Solar Panels

Though the catamaran mounting doesn't allow rotation of the panels fore and aft, as we had on the CSY, we made up for it by adding another 200 watts of solar capacity.

Solar Panels Mounted
Solar Panels Mounted

As with the CSY system, on a good solar day, we are cranking out the amps, and our batteries are fully charged at mid-day on a sunny day, even if we're wantonly charging computers and stuff.  With the excess watts, we can handle several days worth of overcast days before we have to think about charging with other means.  Also, in the wintertime, when the solar days are much shorter and the sun angle is not directly overhead even at midday, we have enough power to run the boat at anchor without running any other charging system.


Alternator Repair

Parts and Tools Needed for
Alternator Disassembly

Parts and Tools Needed for
Alternator Repair

I have taken apart and rebuilt my own alternators ever since I paid about $100 for a rebuild down in the islands that did not work. The problem was that the shop installed 30a diodes in my 150a alternator that needed 50a diodes. Back then I was still trusting third world mechanics with some of the work on my boat. They are real simple to take apart, test and replace parts. See Nigel Calder's Mechanical and Electrical Manual. You certainly don't need to send them anywhere for repair if you have basic tools, electrical skills and first time instructions. If you have one of the older Delco, Balmar or Powerlines, it is fairly simple.

The older Balmar and Powerline alternators look the same, are both based on Delco alternators and most of the parts are the same including the cases. Parts are available many places in the US including some Alternator/Starter parts stores like Royal Battery in Florida and elsewhere. Used parts are available at auto junk yards and alternator shops everywhere. The small case alternators are built with capacities up to 150 amps, over that they use large cases.


Lightning Issues

Here is a bit of interesting info on lightning, its cause, prevention and cure from a discussion on an SSCA forum:

"Actually, lightning is very well understood in the scientific community. How it forms and how it reacts is also understood. The University of Illinois and others have many detailed scientific papers available on the subject. Exactly where and when lightning will strike is a variable as it is part of Mother Nature and there is a reason she is called "Mother Nature" and not "Father Nature."

As to lightning and boats, the issue comes in two parts - 1. Prior to the strike; and 2. During the strike.

Part 1. concerns how to reduce the probabilities of a lightning strike. Lightning is a two part event. The ionized "leader" sweeps an area below the generating cloud and an opposite "leader" sweeps back and forth up from the surface of the earth. When they connect a pathway is opened and the energy is discharged. To a boat the ground/earth "leader" is of most interest. As this "leader" oscillates around it reaches up "x" distance into the atmosphere. Whenever this leader encounters a vertical object like a tree, house, telephone/power pole, or the mast of a boat it can reach further up into the atmosphere and has a better chance of making a "connection." [same thing as tall men in a bar full of good looking women].

So reducing the "electrical" apparent height of your boat is good. This can be done with static dissipators such as the Forespar Lightning Master. (Which is a copy of the static wick principle used on airplanes and airliners). The sharp small "spikes" of the device "bleeds" off ions as they build up and electrically reduces your mast height to equal that of the ocean. However, to do this it must have a "significant" and good ground to the ocean. That translates to 4 square feet of flat plate copper in contact with the ocean and 2/0 welding cable between the mast and the plates submerged in the ocean. A static dissipator will not dissipate if it is not connected with the ocean.

So the result of part 1. is to electrically make your boat height equal to the ocean. If you are anchored close to shore or in the close vicinity of other "unprotected" masts/boats your probability of being hit is significantly lower than theirs. If you are out in the middle of no-where/ocean by yourself you are now "even-steven" with the ocean as to getting a hit.

Part 2. is what can you do to prevent/minimize damage to the boat and its contents during a strike. Again, the 4 sq ft. of copper joined with significant sized welding cable to the mast(s) will provide a highly desirable pathway for the lightning's energy to get directly to its only objective - earth ground. If the mast(s) are not sufficiently well-grounded then the lightning energy will try to find an alternate path to the ocean. If the mast is not available to the lightning, then it will travel down the shrouds/stays to the bonding system and set up a "field" inside the boat that will "fry" most electronics and has been known to heat metal thru-hulls sufficiently enough to melt them out of the hull and you are left with 1.5" holes for the ocean to enter. Lack of any grounding to the ocean and you can end up with holes blown through the hull.

Side note: while your boat is floating in the water it is grounded. When you boat is "on the hard" (out of the water) it is not grounded and any lightning strike to your boat or to a neighbors boat will fry your electronics or other fine metal objects or more serious damage. It is advisable if you are going to leave your boat on the hard, in an area with probable lightning, to drive a copper or steel grounding stake into the ground beneath your boat and hook up a significant sized wire from it to your masts or boat grounding system.

There are many other esoteric factors available to folks wanting to get the "whole story" such as positive versus negative forms of lightning, high frequency vs low frequency lightning, etc. but for the boater I think the primary interest is minimizing damage to the boat, contents, and not curling the crew's hair. This is done by dealing with the before and during aspects of protecting/guarding your boat from the energy in lightning.

Exactly where and when a strike will occurs is not determinable - the same as the actual path of a hurricane or tropical storm is not totally predicable as there are too many variables in nature for even the powerful human built computer to input and resolve. So you can only do what you think is cost-effective to "lower the odds" that you will be the target".

Here is a link with a good discussion of lightning protection systems and the ABYC rules from a custom yacht designer dated 2007-09:

Here's what he says (comparing a 12' strip to a 1 sf plate):

"The ABYC suggests the use of a grounding strip, rather than a plate. The ABYC rule states: 'A grounding strip shall have a minimum thickness of 3/ 16 inch (5 mm), and a minimum width of 3/4 inch (19 mm).' A strip approximately one inch (25 mm) wide and 12 feet long (3.7 m) has nearly six times the amount of edge area exposed to the water, which will improve the dissipation of charges. 'The grounding strip, if used, shall extend from a point directly below the lightning protection mast, toward the aft end of the boat, where a direct connection can be made to the boat's engine'.

A grounding plate, if used instead, should be solid, rather than the sintered bronze type often used as radio grounds. The sponge-like structure of the sintered bronze plates may, in the event of a strike, allow the instant formation of steam, which could blow the plate apart, resulting in possible severe damage to the surrounding hull".

An excellent discussion on Marine Grounding issues (lightning grounds vs radio grounds vs electrical grounds) can be found in Stan Honey's article on Marine Grounding Systems.

My copper bar on the CSY was thru bolted to the hull on the port side running from about the forward main cabin bulkhead aft into the engine room. Two of the 3/8" bolts are nearly even with the mast so that I could get short runs of 2/0 wire to each from the mast without much bend. The connections need to be really solid, so I did the mast thru bolted connections while the mast was out of the boat.

If you Google boat lightning grounds/protection you will find much more info on this, including this useful tidbit on Kasten's site:

"The top-most end, or air terminal, should be a sharply pointed spike. Alternately, a wire 'brush' type terminal can be placed at the masthead, with the bristles pointed upward. There are several claims that a single spike is more effective than a brush for dissipating the charge built up by the boat".

We took both the spike and the bottle brush from the top of the mast on the CSY when we sold it, and mounted it on our catamaran mast.  My spike is 5/8" aluminum, about 18" long. I threaded the bottom so I could bolt it through a web in the mast cap.  Some pics of the CSY setup here:

Of all the scary things about cruising and boat ownership, lightning scares me the most. Not only because of the potential for huge repair expenses, but also because of the very real threat of loss of life. It is a serious subject worth careful consideration by anyone using a boat.