The batteries like being overcharged!

I've noticed that the numbers on my solar controller don't always tell the whole story.

My Lifeline AGM batteries really like being overcharged, hard-core, in bright sun. Even though they say 14.1 volts when fully charged in a dull fog, they aren't as fully charged as when they get to 14.1 volts in the blazing bright sunshine, and are subjected to that for many hours.

So, for example. It was really foggy a few weeks ago. It took me several days of sunshine and very little battery usage to get my batteries up to full charge. But, even then, they'd deplete very quickly! Sure, they'd charge up quickly too, but then they'd deplete quickly. I'd start the night out with 12.9 volts, and after a few hours of computing and Internet, I was down to 12.5 volts!

But then it got hot and sunny for a while. I deliberately parked my van in baking-hot sunshine, day after day. The controller was whining up a storm, and my batteries sat at 14.1 volts for days. Well after all that, I'd start those nights at 12.9 volts alright, but after being up nearly all night on the computer, with the hard drive going and a second Linksys file server going, it'd still be up at 12.7 volts by the time I called it quits!

This morning, the controller was pulling over 12 amps out of the solar panels, charging up those batteries. They got plenty thirsty!

So these AGM batteries have a very long tail on their charging. They get up to full charge quickly, even at low amps, but they really like to be charged up hard, with lots of amps, in order to hold their charge longer. The volts at charging, or after charging, don't tell the whole story. HOW the batteries got to full charge has a lot to do with how slowly they'll discharge.