On Monday, May 18, 2020 at 6:16:48 PM UTC-4, John Foster wrote:
I'm looking for a good charger for my PowerSonic AGM batteries. I have a car charger, but that seems to be malfunctioning, as it doesn't seem to want to charge car batteries or my glider batteries. Any recommendations on a good charger for these type of batteries?

There are so many charger models... I've found that some of them don't quite function as promised, or only work well with certain size batteries. So they should be monitored by a human. E.g., one small cheap charger that was supposed to be smart, when connected to a 12AH battery, never reached the point when it switches from "constant voltage" (about 14.5V) to "float" (about 13.5V), perhaps because the charge current at the high constant voltage never decreased enough in its "view". As a result, the battery got hot, meaning it was overcharged - which cuts short its lifetime.

If you are not in a hurry, a charger that never gets to a voltage higher than 13.8 or so is safe, but leave the battery connected at least overnight to get more or less fully charged.

Meanwhile, SLAs are rapidly becoming obsolete, as LiFePO4 battery prices are falling. Since the latter last about 3 times as many years, they are now cheaper per year, and they have many other advantages. How to charge them is a whole 'nuther topic. Which we may or may not want to drift into here in this thread?