Those aren't really intended for charging batteries. They're for keeping a charged battery from self-discharging, while sitting unused for a while. I tried 3 in parallel, and could get much of a charge to a 7 Ah battery. There are 5 watt panel sold for a similar purpose, I bought 3 off Woot.com a while back ($14.99 each). Haven't had many clear days to play with them. Futurlec has charge controllers, the 5 amp is around $25, will take care of your battery, whether you use it or not...