This device uses a single 15 watt solar panel to charge up to three lead acid automotive type batteries, keeping them isolated from each other - not in parallel. It is based on a BASIC STAMP BS1 and all of the parts are available from Jameco. I use this device to charge the battery in my truck, which is parked in a garage that has no AC power. It also charges a battery to power a garage door opener and a 12 Volt light. The July issue of Nuts and Volts Magazine will have an article about this project.