PD4655 Charging Graph

pnichols wrote:
How much capacity loss per year with an average (Lifeline advertising as being the "best" notwithstanding) AGM battery can one expect if they've treated it "perfectly"?.....

So I'm guilty of being one of the folks who say "They have lasted 8 years come this November". Am I kidding myself that they are still any good? I guess I'll have to break down and load em' up with a 20 amp draw-down rate and see if they still make it to five hours with their at-rest terminal voltage dropping down no lower than around 12.1 volts (it's a 200 AH AGM battery bank).

Phil, your math is screwed up--not like you! :)

You should take 10 hrs at the 20hr rate to get down to 50% SOC not 5 hrs. Voltage at 50% SOC on AGMs is higher than for Wets, which vary between 12.1 (Trojans and some others) and 12.2 (some others besides them)

A 20amp draw down on a 200AH bank is way too high for a 20hr rate. The 20 hr rate on a 200 AH bank is 10 amps. Your 20 amp draw-down would bring Peukert in big time and it would not be half like your 5 hrs but less than that to get to 50%.

You must drink more coffee and get your math sorted out. :)

Back to your post, yes you have been babying those batteries but I always wonder if your definition of 100% SOC is true, which is based on them taking no more amps in at the voltage they are at.

With Wets you can get to there, but then find out the SG is not up to baseline (allowing for SG lag) so you have to up the voltage so they take more amps till SG is up there where it belongs.

I would hate to have AGMs and not be able to do that so I can know my batts are truly full and not at some fake lower amount. You must take Valium or have nerves of steel to own AGMs and be able to sleep at night thinking your batts are ok. :)