Oshkosh Camping - Battery Power

This year will be my 5th consecutive AirVenture. If ever there was a
born camping hater, it's me. But I have slowly gotten the hang of it.
Last year was fantastic, and I have some of the regulars here for the
ideas that made it that way. (Eye shades & ear plugs... how could that
have not occurred to me?)

Having electrical power for Game Boys and my throwaway laptop made a big
difference. Last year I bought one of these to charge a good sized gel
cell:

http://www.goldenpsx.com/image1.jpg

It worked fine but I'm not sure what would have happened in an 'over
charge' situation. Since several of you are expert in electronics and
engineering, can anyone take a quick look at this and tell me if this
unit would be advisable to use between the 12V solar panel (13 watt) and
a 12V gel cell? Not knowing what keywords to search on make this sort
of thing a bit difficult.

http://store.solar-electric.com/sg-4.html

Tom