Stop in for a cup of coffee

So a couple years back, a friend of ours gave me a 30 watt solar panel kit for my birthday. It got put up in the attic and never assembled, found it over the weekend when I was cleaning out the attic. Put it together and right now, it seems to be charging my truck batteries that i pulled the other week. Has a built in charge controller so I’m curious to see how it all works.
I have this cheap solar panel, 6x12” or something. I connected it to a lawn tractor type battery that runs a small 12 volt demand pump to supply water in my office. It has kept that battery up for years.