This was pulled from a boating site , but might help folks starting out with batt knowledge
LA lead acid, FLA Flooded LA AGM absorbed glass mat LFP life pro
LA batteries have a charge voltage limit specified by the manufacturer. You cannot simply run the voltage up higher to maintain the charge acceptance rate without damaging them, and their acceptance rate tapers even at high voltages. All of this is well covered on
Rod Collins site and many other places.
FLA batteries operated between say 30 and 80% of SOC are pretty efficient - the acceptance rate is high and you can equalize them periodically to drive the sulphate back into solution to recover the lost capacity. Prior to AGM and LFP that is what people did to minimize charge time.
AGM have a higher initial charge acceptance, but require full recharge more often to maintain capacity and you cannot equalize them to desulphate, as they will dry out. (FLAs dry out too but you just pour some water back in). To get to 100% SOC on AGMs (or FLA) requires about a 4 hour charge tail AFTER you have gotten to 80%.
LFP will continue to take the full charge right up to about 98% SOC. That difference may recharge LFP faster, even if you have a limited charge source. For example, if I have a 50 amp source, and I am down to 50% on my 200AH AGM (-100 AH) it will take 50 A for an hour (back to 75%), then slope down averaging 25 A for the next hour (back to 87%), then taper to near zero over the next 4 hours (back to 100%). 6 hours to full. The LFP would accept 100A if I had it, but I don't, so it gets 50A. It accepts that for 2 hours and I am back at 100%. If I had a 100A source, the AGM might accept that for a few minutes, but reaching full will still take maybe 5.5 hours. On the LFP, 1 hour. So yes, the LFP benefits from the higher charge capacity more, but it charges faster even from the limited source.
FLAs operated between 30 and 80% would also take the 50A for most of the charge time but would not accept 100A so similar to LFP if charge is limited but does not benefit from a larger charge source.
The weak point of AGMs is the need to fully recharge them frequently or you will kill them. You have to balance that against their benefits: typically lower internal resistance, don't outgas acid and corrode everything, don't require watering, much lower self-discharge rate, do not spill when tipped over, and longer cycle life
if properly cared for. If you and your charging system are going to mistreat them, you are better off with FLA, as they tolerate abuse better and are cheaper to start with. For most boats that are used weekends and plugged in during the week, AGMs are ideal (with a good charger). Living on the hook and trying to minimize charge time, AGM only makes sense if you have some persistent low amp charge source like solar to finish the charge tail. Otherwise run FLAs from 30 to 80% and equalize when you can. But LFP are ideal for that use, charge quicker, last many more cycles, and don't care about full charges.
My own use case on my trawler favors AGM: I move nearly every day with a 4 - 6 hour engine run. The AGMs get fully charged nearly every day. The only benefit of LFP would be lighter weight and longer cycle life. But the use case on my sailboat favors LFP: engine is rarely run, when it is it drives a 7 KW alternator (equivalent to 560A at 12V) and I want to charge quickly and infrequently.
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