LiFePO4 house batteries

[CapnR]

in my case it would be 11k to replace all of mine.

Alright Botjem, I'll bite - 11?

So, part of my job is to manage a fleet of batteries (roughly 10,000, and ranging 8,000-15,000 Ah). These have been Lead Acid technology, with a Battery Management system on each battery that monitors state of charge, cell temperatures, ambient temperatures, and resistance to applying a charge. We also manage equalizations across cells, to try to get as much life out of them as possible.

There are 3 reasons for lead acid batteries that do not last 5-8 years. I typically get 8 years, although I have had a few fail earlier than 5 over my 35+ years of boating.
1 - Check water levels monthly and when away from shorepower monitor battery state of charge.
2 - Never let your lead acid batteries drop below 30% state of charge; if you are eating them up, add bank capacity or run your generator when they deplete to 50%.
3 - Replace the entire bank of batteries at the same time. One battery at 50% paired up with a new battery will get you through a season, but you're killing the new battery.

I bought my boat in Dec 2019. The first thing I did was pull the batteries and assess what I had. The previous owner had one battery from 2014 (capable of 50%) paired up with a battery from 2018 (80
%) on the starting bank. And the generator battery was from 2015, (showed 40%, but high enough in capacity to start with ease). So I ditched the 2014 and 2015 batteries, replaced with (2) new series 27 batteries on the starting bank. I then redeployed the 2018 (again, 80%) from the starting bank to the genny.

The house bank (3 series 27's from 20188) were consistently about 70%, but several cells were low on water. I topped them off and ran them frequently last year; this year they're about the same. I'll probably need to replace the house bank in 2 years.

Compare this with a buddy (1996 390 SR Express) that always has to run his genny at the swim hole. He says he only gets one or two seasons out of his batteries, despite the fact that I know he's always checking the water level. Got into his bilge, didn't have to ask a single question. (2) series 27's that he expects to run the whole boat. Poor guy doesn't have a chance.

Sorry for the book, but now onto Lithium Ion batteries; huge gains in clean power, all the way down to 5% without affecting battery life. We stayed away from the LiFePO (Lithium Iron Phosphate), in favor of the NMC (Nickel Manganese Cobalt). This was back when Samsung was getting thermal runaway; we're now reconsidering with the improved cell monitoring and management.

Here's the so what:
We are seeing ZERO maintenance, and any failures in the field are sent to the battery Mfr for repair. This is because their Battery Management system is designed to eliminate the potential for abuse. Below 5% SOC and it shuts itself down to prevent damage. Same for high temp events. We are eliminating watering and equalization programs, because these are not required for Lithium batteries. We are also able to dump CRAZY amounts of power to them when charging. We have 40V batteries with 700Ah capacity. When charging we are able to dump 500A into the battery without creating excessive heat (not exceeding 125F). And the batteries actually cool when you are pulling power from them.
We are being told that we will be able to achieve 3000 - 5000 cycles (cycle is defined as 95% of the capacity), and after these cycles they will still maintain 80+% of their original capacity. This opens up a huge opportunity for secondary markets.
In boating terms, this means that with an appropriately sized setup, you should be able to discharge your banks to 5% 3000 times. And if you are overcapacitized by 50%, that means 50% discharge for 6000 cycles.

If you live somewhere that you have 12 months of boating per year, that means that you will get 3000/365 days per year = 8.3 years if you discharge 95% every day before recharging.

For me (Michigan), I get about 61 days of use (5 months, 8 weekend days + another 3 weeks trip). At 95% discharge every single day, that battery will last me 3000/61 = 49 years. If I believe the sales guy (5000 cycles with no degradation), well, you can do the math.

What we really want is to get our hands on some large Lithium Ion batteries in 10-20 years, because they will still outlive me.

The market will either move to lifetime batteries direct from the manufacturer, or a highly discounted battery that is manufactured with a life of 800-1000 cycles.

With respect to weigh savings, I know that every bit helps. But it would save me 120#, if the replacement charger weighs the same as my current one. By and large, I think I've typically got 120# of backup beer and water buried in the bilge. Not worried about it.

The other thing I always ask is whether the battery is UL listed (we specifically require UL1642 and UL2580). Be very cautious and ask a lot of questions.

The real fun topic (for another day) is the potential for retrofit of our gas or diesel powerplants to electric . I now yield the floor, as I've hogged it for far too long.