Lithium Iron Phosphate (LiFeP04) batteries

D

Dwane Goodell

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Sep 10, 2026
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Location
Seattle
C Dory Year
2006
C Dory Model
22 Cruiser
Hull Identification Number
CD022321G506
Vessel Name
Dog House
I’m researching converting to LiFeP04 batteries. The price has come down and they weigh less than half, but it’s NOT plug and play. Has anyone done it?
 
"Converting" to LiFePO4 has two paths, house and starter batteries. I started buying and using LiFePO4 batteries when they first came out and were extremely expensive, due to high capacity and low weight to run trolling motors with my canoes and kayaks. I had used Pb types for years for the same purpose. Yes, LiFePO4s are much cheaper now. LiFePO4s are great as trolling motor batteries, as they saved my back and gave more Watt hour per pound. When people say "plug and play" you typically mean replacing the starter battery. Historically, LiFePO4 are used to replace "house" batteries used to run electronics, fans, diesel heaters, etc., but not start motors. The most common problem with using most LiFePO4 batteries for starting is instantaneous cranking power. There can also a problem of charging LiFePO4 batteries in extremely cold conditions, but I don't think cold-weather charging is what you are going to see as a problem in marine areas of the PNW. Generally, LiFePO4 battery types are not designed to deliver the amps required to start motors. There are LiFePO4 models that say do (i.e. Dakota), and the general consensus is still that they don't work great as starter batteries either. Though I can't find that he addressed this issue directly, Will Prowse found that many batteries don't deliver the instantaneous amps they promise. Currently, I have two 460 AH 12 volt Epoch LiFePO4 batteries as the house batteries on my CD22 and a sealed lead acid as the starter. With jumper cables, I find that either Epoch will start my Honda 100 outboard just fine. They state they can put out 1300 A for 1 second, which is normally sufficient. Obviously, the Epochs are too large to fit into the normal batter compartment at the rear stern, so are physically not "plug-and-play". I have about a dozen other 12 volt LiFePO4 that I used in the C-Dory before the Epochs. Neither the Battle-Born, Li-Time or Renogy 100 amp LiFePO4 will start the motor with the starting motor unhooked. The internal battery-management systems shut them down. My conclusion is to use the Pb-acid as the starter and LiFePO4 for house batteries. Others may have seen better results. Good Luck.
 
I have not done in it my boat, but I have in a converted van. The two biggest issues are very high discharge currents and high charging loads.
While cranking, you can pull lots and lots of amps but for a brief period. Li batteries don't like this much.
Li batteries can have a very high charging current even for moderate amounts of discharge. Most alternators cannot handle the load without overheating or burning up.
Currently, the best solution is to have a FLA battery for starting and motor loads (high current, short duration) and a Li battery for house loads (low current, long duration). A DC-DC charger between the engine side of the system and house side will limit the charging current to the Li battery to protect the alternator and can prevent the Li battery from pulling down the start battery when the engine is not running.
While they have started marketing Li batteries that are marketed as drop in replacement and are a supposedly ok with cranking motors, these batteries still have the charging current issue. You'd think that they'd make a Li battery with a BMS that will limit the input current to a reasonable amount so that stock alternators can handle them. But the battery has the same input and output lines so maybe having a BMS that can control the input current differently from the output current is too hard. This could be solved by having a BMS with different connections for charging input and battery output, although this might make electrical system design more complicated.
I have considered converting the house side of my boat to Li. However, the way my boat is currently wired (everything is fed from the FLA battery system) would require a rewire job to separate the engine side from the house side of the electrical system. While this is doable, I have not been motivated enough to do it yet.
One other thing to consider is that if you have a high Ah Li battery and you depelete it regularly, how are you going to charge it back up? On a CD 22 there is not a lot of room for solar panels (which on a good day will give you maybe 200w for part of the day). Most CD22 size outboards will only have about 30-35 amps spare overhead for charging (through the DC-DC charger). If you have a 300-600 Ah Li bank, you'll need to spend a good amout of time charging if you use a lot of that capacity.
 
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Thank you both for these very comprehensive replies. My, new to me, C-Dory came with 3 correct group 24 AMG batteries. One is new, the other 2 are 8 years old (salesman trick). My path of least resistance is to simple replace the 2 old ones with identical new ones, but the 100 pounds of weight savings is hard to ignore.
 
For our last C Dory 25, I put in two Battle Born 100 amp hour batteries to run my chest type freezer and chest type of refrigerator. They also power my microwave. These were placed under the Port side of the V berth. The Stb side had a Victron 2000 watt Inverter, 80 amp charger/50 amp boost settings. I put in guages for these in the galley area. I kept the group 24 engine start and another group 24 for lights and electronics. For charging the LIFePO4, I used a Sterling Bat to Bat 30 amp charger set with a profile set for the LIFePO4 battery. This worked well.

I have two ongoing experiments. One is a 100 amp hr LiFePO4 in a group 31 battery box, a 10 amp 120 volt mains charger, a 15 amp Victron bat to bat charger with clips to any vehicle's starting battery and a 1000 watt inverter. There is a 12 v plug for a chest type 40 liter chest freezer/referigrator. This fits in the back of either of our SUVs daily drivers and will keep food frozen on the way back from the grocery store. I use a cheap chinese knock off of the Victron 702 meter, This works well.

The second experiment is a bank of six 100 amp hr. LiTime LiFePE4 batteries, and 1200 watts of solar panels, with proper Victron electronic components, using Anderson plugs. I also have a Victron 3000, with 120 amp charager. This is a back up if we loose both the mains power and both our back up generators: 1800 KW natural gas or 7500 gasoline generators. Proper isolation switchs are in both of these setups to avoid feeding hot 120 volts into the mains system. We have not had to run this in an emergency, but only did tests. This will run two refrigerators and one freezer, plus some 12 volt lights and chargers for items like computer, I pad etc. We have frequent power outages at our home--last night for 2 hours as an example. The Natural gas generator kicks on in about a minute, and we have power packs to run our security system, so that never looses power. This is a stationary system because of the size of the battery bank and the solar panels. Theoretically it should cover the intended emergenvy load indefinately. The batteries and inverter are hooked up and kept charged. I would have to manually cut in the swith to isolate these appliances and direct the 120 volt power to only these units. The solar panels have to be deployed and cables run to the battery system. But these being fully charged they will carry the intended load for at least 24 hours. Most likely this woud be needed after a direct hit from a hurricane. In the past once we only had the 7500 watt gas generator. We had to store 50 gallons of gasoline, and refill after a week or so. Then we added the Natural Gas generator, and every time it has come on so far. But if there is a wide range power outage, tree roots breaking the natural gas line etc. then the natural gas might not be available.
 
There have been issues with some Battle Born batteries overheating and melting internal components. If you are thinking of this brand of battery, do your homework.
 
I agree with the previous comments about using LiFePO4 for starting, and the problems with charging them from an alternator. BUT you also need to look "under the hood" before purchasing any. There are so many brands out there, especially on Amazon, that one often doesn't know where to start.
1. Make sure the cells in the battery are listed as Grade A or " EV grade". If there is no mention then it probably means they are Grade B and will not last as long as Grade A.
2. Make sure the battery has a bluetooth connection to an app on your phone that lets you monitor each individual cell. I have found that after 2-3 years the cells can become out of balance even in the best batteries. This is because the balancing current used by the BMS is often too low to compensate for differences among cells. Most balancing currents are on the order of 100 mA and I have found that it needs to be at least 1A, even assuming you fully charge your battery at least every other charging cycle. I would stay away from any batteries for which you cannot find the balancing current.

I found I had the same problem when I was building my own battery bank from individual LiFePO4 cells. After 2-3 years the cell balancers that were then available no longer were able to fully balance the pack.

After 3 years of cruising, all four of my Bestgo batteries are not fully balancing the 16 cell. The BMS shuts down charging when one cell reaches 3.75V. However, as shown in the screen print, cell #9 is still not fully charged. I bought my batteries at a time when they were only providing 100mA of balancing current. They now have changed that to 1A, and because my batteries are still under warranty, they are sending a 1A balancing module that I can add to the BMS to fix this problem.

That is another nice thing about these Bestgo batteries: The top can be removed and the battery serviced.

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Just my opinions,

Doing your homework is relatively easy because Will Prouse on YouTube has done most of it for you. He's taken most of the LiFePO4 apart and shown you what is good and what is not, and tells you, depending on your use what is good and what is not as far as using that battery. Been watching him for years and he's actually fun to watch and hugely informative.

On my boat I use a Sam's Club Duracell deep cycle group 27 for my starting (I know, I know!!! I've done it in the past and get a good 5 years out of a $100 battery for starting my engines) (same battery, different label, as so many other deep cycle batt's like WM's). For the house bank, I use a Humsienk Mini 314A Smart battery ~$460 and then, when I installed it, I made sure to address all of Will's concerns with that battery by, installing a 70A battery terminal fuse and not connecting it to another battery in series or parallel. I bought a Li charger, but have only used it for it's first 100% charge and then hooked it up to my 450W solar panel. The battery is barely larger than a group 31 and lives in the starboard rear locker right next to the Duracell athwart-ship with the new engine battery switch attached to a piece of ply epoxied to the stern of the locker. Works great!

I did a complete re-wire on the boat, but working with the wiring installed on these boats is super easy... My battery switch was located in the aft locker already so on my boat (had the wiring been sized properly and had the wiring been marine grade tinned and had my wiring been fused properly) if I would have just pulled the house wire off of the main switch (usually #2) and only left the engine + cable on that switch with the switches common cable going to the starting battery. The house cable would then go on top of the Humsienk + battery terminal fuse and the negative cable for the house going to the negative terminal as well as the neg jumper cable between both batteries negative terminals. I then would have done what I did with my new wiring and put a main battery switch for the house in the lower right corner of my dash under and to the right of the enclosure for the wiring. My solar panel then goes the a Victron smart regulator and back to a second, 40A terminal fuse on the Humsienk. Very straight forward.

Now, I did change out the solar panel after my Bahamas trip to a Cigs 200W, taped on roof (looks way better and doesn't have a thin aluminum frame to tear apart!) and I think that's still plenty enough charge for my needs. If for some reason it turns out lacking, I'll install a Victron Orion XS 12/12 50A DC to DC charger because that's the only one, at this time, that allows you to custom set the max charging amperage. I would then set the amperage max for 25A because the Honda alternator only has ~30A-35A amp capacity left over after taking care of it's own needs and I don't want or need to have the alternator maxed out for long periods of time. Like everything boating, they'll be many opinions, but this works well for me and I'm very comfortable with it.
 
FrankisCaptainBobo; I'll be very curious about how well your CIGS panels work when it gets really hot. I have three basic mobile installations 1) 2x175 watt Renogy flexible panels on my CD22, strapped on with ventilation underneath, 2) 2x175 watt Renogy flexible panels glued down to an aluminum roof (no underneath ventilation on my 4-wheel camper, and 3) 3x100 watt CIGS glued down to the aluminum roof (no ventillation) on my Alaskan camper. So far, the CIGS seem to perform well both in shade and when it gets really hot compared to the regular flexible panels. Obviously, partial shade isn't likely to be a serious problem with a marine application as you don't usually anchor under trees, and I do have my CD22 panels with ventilation between the panel and fiberglass roof.
 
robhwa said:
... Obviously, partial shade isn't likely to be a serious problem with a marine application as you don't usually anchor under trees, ...
Click to expand...
On boats things like radar units, radio antennas, masts, and booms can shade a solar panel. Some solar panel designs will significantly lower their output if any part of the panel is shaded. Anti-shading type solar panels are less susceptible to this. Its got to do with the number of bus bars in the panel and how the cells are connected together.
 
Another option for the DC to DC charger may be the Sterling BB1230-12 Volt, 30 Amps - Pro Batt Ultra Battery to Battery Charger. This has a specific charging profile for charging a LiFePO4 battery from the 12 V engine start battery. It limits to to 30 amps charging. I used this in the C Dory 25, circuit in my post above.
 
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