Evan: I get good service (several years) out of the batteries that I take home between flights and charge right away (and then disconnect from the charger). The battery that died was the one I left in the trailer all summer. It was fairly old even before I used it for that purpose. I would have just assumed it died of old age. But, the club batteries died too. And they were only 1 year old, that's annoying. And I don't really know how often they were left in the gliders. (Nor how good are the club chargers that they get left on for long periods.)

If we were to switch from SLA to, e.g., LiFePO4 batteries (as you have), will they survive the heat for long? How long? They cost about 5 times as much... And the promised large number of "cycles" is irrelevant if they too die after a few years due to age alone. We only subject most batteries to dozens of cycles per year.