A circuit to use 2 single cell li-po / li-on batteries in series and charge them in parallel

I was looking for an option to create a circuit with a switch, so I can use two single cell li-on Nokia cell phone batteries in series, but charge them in parallel through a USB charger. The idea is to be able to install the batteries in a small robot, where they will not be easily accessible to charge with my regular li-po battery charger. I have a couple of these simple but effective battery chargers lying around, but they can only charge a single cell. After some digging around, I found the…continue reading →