Inverter battery replacement

I've been reading threads about lithium batteries in several fora for years... and I've drawn about eight conclusions.

1) LiFePO4, aka LFP, is the only safe chemistry for marine use... and it's apparently even slightly safer than lead-acid including AGM if done right.

2) LFP has become less expensive than lead-acid, including AGM... for the long run. For this to be true, you've got to use boatloads of battery cycles.

3) There is LFP and then there is LFP. Quality is slightly all over the map. Cheaping out isn't useful.

4) The set-up (the "if done right" part) isn't hugely complicated BUT it's gotta be done correctly.

5) The specific BMS -- Battery Management System -- is a big deal. And there's some stuff about managing float voltages, since LFP is happiest when NOT charged to 100% all the time.

6) LFP needs less space for capacity equal to lead-acid. Or... you can stuff more capacity into the same space as a previous lead-acid bank.

7) LFP is happy with house loads and inverter loads. Not so much with starter loads or thruster loads, maybe or maybe not windlass loads. More recently, some LFPs seem to be becoming more comfortable with start-like high-current loads. Sometimes, it's the BMS, not the battery, that causes any inhibition here.

8) An LFP conversion would NOT/NOT be a DIY project, for me. (See #4.) I dunno enough to be comfortable with the installation and fusing of ANY new battery system, and LFP would be adding a layer of complexity over and above that. Not unlearnable, I just don't have time/inclination.

There's a lot of "it depends" in all that, though.

When we got this boat, I wanted an inverter. We have three main 24V battery banks, one for each engine and approx half of the DC house loads. One for bow thruster. Latter is under-utilized, and also already located semi-near our AC/DC panel. Voila, it became our dual-purpose inverter/thruster source. (BTW, the MultiPlus we installed is an inverter/charger... not just an inverter.)

I would have converted to LFP for that, except there weren't really any LFP batteries that could deal with the high-Amp thruster current requirements (560A for 4.5 minutes). So we instead upgraded the PO's crap (and old) lead-acid batteries to Lifeline AGM 8D pairs. More recently there seem to be LFP options coming to market that could deal with this... maybe.

Our AGM-based inverter/charger system based on ~255 Ah @ 24VDC works fine with our constant inverter loads (when away from shorepower or with genset off) -- AC-only galley fridge and freezer -- for about 12-ish hours. We haven't done much analysis on how other temporary loads (TV, microwave, coffee maker, etc.) might affect that. I think an LFP alternative could likely at least double (maybe triple) that within the same battery footprint. In our case, at anchor with an electric cooktop, we need to start the generator to cook dinner anyway... so we just recharge and heat water during meal prep... and it's all "good enough."

In a previous boat, we converted a battery bank to Lifeline 6VDC AGM golf cart batteries to service inverter loads; that worked well. We were space-limited, but I was able to put in two pairs -- so we could still re-cable for power if one battery crapped out. Even better might have been the taller L16s, but we didn't have enough available height for those.

FWIW, we tend toward AGM (for lead-acid) to mostly eliminate maintenance and to reduce off-gassing. Otherwise, wet batteries can be very cost effective. In our case, Odyssey AGMs (previous boat) lasted 11-12 seasons, probably partly due to light use away from the dock. We don't have long-term data on the Lifelines, yet -- previous boat inverter bank, and three banks on this boat -- but they at least have a similar rep as Odyssey.

-Chris

Someone is making Solid State, the problem is the voltage is too high for most applications IMO. But a 12v batteries nominal voltage is 14.4 and rated voltage is 16.4 volts.
solidstatemarine.com

I have 2 banks of Lithium in my boat, but it's a 20' flats fishing boat. A Dakota 36v 60 AH trolling motor battery which weighs 44lbs and replaced 3-75lb group 31 AGM's and lasts just as long before needing a charge and a Relion 12v 100ah for the house/emergency start battery. They have been flawless. Lithium REALLY works well in a trolling motor or house battery setting. You can get a 12v group 31 Dakota 320 AMP HOUR single battery or a 640 Amp Hour in a 8D case. You can hold a ton of energy with much lighter weight and much less space. They take a charge much faster and can reliably use 90% of the capacity and they last 7x as many cycles. I think if you stick with a name brand lifepo4, your chances of fire are pretty low.

Near as I can tell, there's never yet been a documented case of fire caused by LFP batteries. Which is not to say I've read everything about everything, of course...

The BattleBorn thing is getting significant critique from trawler folk, too. For those who haven't seen, these videos seem to describe the issue:




Apparently no fires. (Known of? Yet?) Which I guess (?) means the BMS is doing its thing properly.

There's also this:
"A Ford (or Chevy or Cadillac or whatever) engine has a problem... therefore all engines have a problem."
That kind of reasoning seems to be not-uncommon within the world of batteries... and apparently sometimes the chemistry takes the blame for everything.

J posted the link to the Solid State versions. It's not easy to find it, but eventually getting past their "better than lithium" hype they do admit the batteries are LFPs... but and it's the electrolyte that's solid. One of their big claims is about being able to handle high current requirements.... and we know of a user who's starting Volvo D12s with them, apparently all good.

Can't say I'm for 'em or agin 'em... ref any of the chemistries. Seems to me choice depends on goal and circumstances.

-Chris