My Dad is putting together a small PV system. He already has 250W of PVs, now he wants to spend around $1000 on batteries.
He doesn't want to have to water them, and wants to store them outside where it can get below freezing, so he's interested in AGMs. He wants to get 4 of the Diehard "Marine" ones, at $250 each for 100AH. That seems really expensive to me.
He's had a small 40W PV and has been using two Diehard 50lb lead acid "marine" batteries, one at a time charging the other being used. He swaps them by hand. He doesn't really understand about not running them down too far, and it seems like they only last him a few years. His inverter will shut down, but he also has some DC uses that he really drains them with. I've tried telling him to not do that, but he keeps doing it anyways. I think I've heard that AGMs are even more susceptible to damage from abuse? He'll hopefully be just using his inverter now that he has more PVs and won't run them down as bad, but you never know.
So, I guess I'm looking for a good price on AGMs, so I can get him to spend less, and I'm looking for advice on the longevity of AGMs, and perhaps some info I can use to convince him that quality lead-acids will really be just fine. Or perhaps LiFePO4 would be an option when compared to the expensive Diehard AGMs?