I have this little SLA battery that enables my emergency generator to start without using the pull cord. I don’t have a maintainer on this batter (and maybe I should), so every once in a while I like to charge it up if it hasn’t been used in a while. The initial battery voltage when I started this time was 12.1V, which is actually a bit low for a 12V battery.
The side of the battery specifies: “Constant voltage charge cycle use 14.5-14.9V. Standby use 13.6-13.8V. Initial currently less than 2.16A.” I set the power supply to 14.7V, and set the current to 1A — so a max of 12W, just to be safe. It started off drinking about 750mA and that slowly and steadily increased to about 950mA before starting to trend back down. When the currently drops down significantly, I’ll stop.
I’m using a Korad KA3005P bench power supply and a MightyMax ML7-12 battery. The power supply cost me $140 from Amazon.com in May 2021, and it’s been working like a charm. The battery was $70 from Walmart in October 2021 and it’s also been holding up nicely (very minimal use).
I did the same thing with a larger 35 Amp-hour MightyMax battery with equally good results. The battery was reading about 12.2V when I started. It initially drew about 2.5A and then slowly over the course of about six hours that current started to level off. It’s a 35 amp-hour battery, so I waited until after the current draw was less than about 0.7A before reducing the voltage to 13.7, which is the maintenance voltage. It was probably considered fully charged at that point already, but I left it on a bit longer until it drew about 0.409, when I removed it and put it back into service. The battery read 13V at this point.
