I knew my eight-year-old Concord Sun-Xtender AGM batteries were approaching the end of their usefulness. They had been taking a lot longer to reach float and they were reading around 12.5V before sunrise instead of their usual 12.7V. The shorter days of winter are approaching, making getting through the days more challenging. Then, when I woke up in the middle of the night a few days ago, the voltmeter read 12.1V, with the fridge cycled on. Not good, even though it returned to 12.5 when the fridge cycled off. Time for new batteries.
I briefly considered LiFePo like all the cool kids but, besides the higher price, there would be the hassle of reprogramming my solar controller. So I'd go the easy way and get AGMs again. Sun-Xtenders like mine are about $340 each. Mmmmmm, seven-hundred bucks would be a tough bullet to bite right now. So I decided to go with a couple of Universal brand at half the price. If I get only half the life out of them, I'll still break even.