[C320-list] Converting to LiFeP04 Battery

[Mark Seyler via C320-list]

My old Interstate SRM-4D batteries have died, and I am exploring the
possibility of converting to LiFeP04 batteries. I realize they need a
completely different charging profile than my old flooded lead acid
batteries. That could be accomplished either with a programmable DC/DC
charger connected to a FLA start battery, or by converting my existing
internally regulated alternator to use a programmable external regulator.
Does anyone have any experience with either approach?



I have an upgraded 80amp Lucas Model LEA0437 alternator that I bought from
Parts4Engines several years ago. From what I can see on-line, there are
kits made to convert certain auto alternators to use external regulators,
but I have no idea where to find a similar kit to convert my marinized Lucas
alternator.



I have a Victron inverter charger that can be programmed to charge LiFeP04
from shore power, so that's not an issue either way.



Any good info would be appreciated!



Mark Seyler

S/V Reality,

Catalina 320, #232

New Orleans, LA

[Joel Krauska via C320-list]

I just recently swapped out one of my 4Ds for a 230AH LiFePO4.

notes here:
https://github.com/jkrauska/graceElectrical

I can find some pics if you have specific questions or want to talk more
about it.

Biggest effort was running thicker cables between charger in locker to the
battery.
(to support running it as an inverter and in theory being able to run the
microwave or other high wattage things on battery)

[Jack Brennan via C320-list]

Hi Mark:

The complexities and uncertainties of lithium scared me off a few years ago when my battery bank died.

I found it difficult to understand which batteries were good deals and which were crap. The techie people who were early adopters also loved to create incredibly Byzantine systems that looked like disasters waiting to happen.

I ended up buying four golf cart batteries at Sam's Club (Duracell, I think) that provided me with 460 amp hours for about $400. They're still going strong after three years and can last several days at anchor even when cloudy conditions hamper my solar panels.

If you go ahead with lithium, I would spend a lot of time researching various brands of batteries. There is a lot of junk on Amazon from Asia these days, everything from batteries to stainless steel parts. An off-brand "deal" could be a disaster.

I would also use the DC to DC system as opposed to going down the rabbit hole with exotic alternators. Solar would be a good main charging choice because quality MPPT controllers can handle lithium.

Good luck. I await your updatwes.

Jack Brennan
Sonas, 1998 Catalina 320
Tierra Verde, Fl.

________________________________
From: C320-list <c320-lis...@lists.catalina320.com> on behalf of Mark Seyler via C320-list <c320...@lists.catalina320.com>
Sent: Wednesday, February 25, 2026 5:27 PM
To: C320...@Catalina320.com <C320...@Catalina320.com>
Cc: mse...@cox.net <mse...@cox.net>
Subject: [C320-list] Converting to LiFeP04 Battery

[Charles Martin via C320-list]

I have not yet checked my BoatUS/Geico insurance policy; however, I
recently heard a podcast that claimed many boat insurance policies do not
allow lithium batteries. I am curious if this is indeed a concern. At a
minimum, read the fine print in your insurance policy.

Best,
Chip Martin
S/V Bonaventure, Sail No. 767
(410) 231-0199
chipr...@gmail.com

[Troy Dunn via C320-list]

Mark

The expert on a lot of this stuff is Rod Collins. Goes by Mainesail, and
has a website called marine how to. I think every one of your questions
has been thoroughly covered be an article or two of his. He used to run a
marine electronics business and web store prior to an unfortunate stroke.
He still manages to keep the site up and running last I checked.
Defitnely should have a look there.

Like Jack, I looked into this 6 years ago and opted for GC2s as well. But I
would not let that dissuade you at this point. I also wouldn’t start
messing with your alternator. It’s not designed for continuous output so
you are better off setting it up with a single AGM for starting the engine
and charging as is, and then go DC-DC over to the LiFePO4 battery from the
DC-DC. Try to set up your DC-DC to have the alternator somewhere at about
60% output. Beyond that you would be buying a new alternator soon.

As far as Asian batteries…sadly, it is the expensive U.S. made brand that
turns out to be a fire hazard and a flaming PR disaster to boot. Will
Prowse is a YouTube guy that tears apart any LiFEPO4 battery he can get his
hands on and does very thorough testing and reviews. He’s sorta become
the expert on these things just be being thorough and diligent with his
testing. Between Will and Rod, I would try to get as much knowledge as
you can from their sites and make the best decision you can. I think a
hybrid AGM and LiFePO4 bank may be the best of both worlds now and will
easily fit in the normal C320 spot. When you are sizing your bank
remember that Li batteries can be drawn down to about 10% without any harm
so the size battery you need is almost half that you would require for a
lead based battery bank. 200Ah of Li is like 400 of lead.

Good luck

Troy Dunn
Hull #514

[Bruce Hunter via C320-list]

Chip,        Boat U.S. - Geico is fine with LiFePO4, I checked a couple weeks ago. I decided to go all victron but go with 4 Trojan T-105 AES AGM batteries since my 2005 Catalina 350 (I'm a former 320 owner) had an old Charles 5000 charger and 2 4D batteries. with no inverter. I figure I'd update my system using Victron parts that can be used if I go with LiFePO4 in the future, hopefully the technology will improve to where the required system doesn't require so many parts, or at least I now have a few years to REALLY brush up on things.
Bruce HunterFormer 320 owner ("Nautitime"), current 350 owner, )"Miss Sea-ducer").

Yahoo Mail: Search, Organize, Conquer

On Wed, Feb 25, 2026 at 8:09 PM, Troy Dunn via C320-list<c320...@lists.catalina320.com> wrote: Mark

[Randy B via C320-list]

Mark,
I converted to lithium last year and it's the best thing I ever did. I put
in a Victron Multiplus II 2 kva inverter / charger. I installed it in the
aft starboard dinette locker where one of my FLA batteries used to be
instead of the aft port cockpit locker. I replaced the FLA battery in the
forward starboard locker with a single 460ah lithium battery. This kept my
large cable runs very short and saved a ton of money on large cables.

I didn't opt for an external regulator. I'm using the stock Hitachi
alternator which is capable of 60 amps with a 50 amp Victron Orion XS 12/12
DC-DC charger. The beauty of that device is, you can set the output
current. The Hitachi alternator can only charge at about 50% of its rated
capacity without getting too hot, so I set the DC-DC charger to output 30
amps. In your case, you might be able to use the full 50 amps from the
DC-DC charger. I really have a Hybrid system with a regular FLA start
battery and a Lithium house battery. I have 900 watts of solar on a solar
arch so my engine is just my backup charging source.

You can look into external regulators, but be sure that your alternator can
really output the full 80 amps or it may not be worth it. The DC-DC
charger may be the way to go.

As Doug mentioned, check out Rod Collins site. I got the hybrid idea from
his site.

Randy

[Mark Seyler via C320-list]

Thanks, all, for the quick responses!

Joel, your documentation is outstanding! It may take me the rest of the week to absorb it all. I have scribbled out a schematic that already includes much of what you have done. The crazy part is that the battery is only about 1/3 of the total cost of my materials list! So I'm trying to figure out if there's any way that my approach could be simplified.

Chip, my insurance policy with Progressive does not contain the words "lithium" or "LiFePO" anywhere, so I think I'm OK there.

Troy and Randy, I have read MaineSail's articles on LiFePO conversion multiple times, and get a little more out of them with each pass. I'm looking at a WattCycle 314AH battery in large part because he recommends that brand as the "economy" option, and the 314AH BMS is rated to handle the maximum 216A current my Victron inverter/charger could pull. (I'm too cheap to go with the Epoch brand he says would integrate more closely with my Victron gear). I have also looked at multiple tear-down videos of the WattCycle batteries from Will Prowse and others, which are generally positive about the construction quality. I've seen some complaints on-line that the WattCycle BMS doesn't play well in parallel battery banks, but I don't think I need more than 314AH total for house batteries. I have also seen complaints that the WattCycle Bluetooth app is buggy, but I already have a Victron shunt and display that will report most of the same information as the WattCycle Bluetooth app.

As far as protecting my alternator, that's one potential up-side to an external regulator, since it can have a thermal sensor on each of the batteries and alternator, and rate the current down in real time as things get hot. But I'm not sure where to start looking for a kit to convert my Lucas Alternator to use a Balmar or similar external regulator.

Randy, you're right that the potential benefit of regulating the alternator depends on how much it could produce without overheating, and I don't know how to find that out in advance. But if I could just split the alternator charge line from the starter circuit and send the alternator current straight to the LiFePO battery, and use a lower cost ACR or low amp DC to DC Charger to charge the start battery (which can't take that much current anyway), that could potentially save me a couple hundred dollars worth of Buss bars, switches, and 2/0 battery cable pigtails compared to the schematic that I initially designed to allow me to manually connect either the LiFePO house battery or the lead acid start battery to any load or charging source. And it would simplify operating practices as well.

It's a lot to consider, and I'm trying to avoid learning the unintended consequences after the fact.

Again, thanks everyone - this owners list is a tremendous source of good information!

Mark Seyler
S/V Reality,
Catalina 320, #232
New Orleans, LA