Hi I was just on vacation and forgot my camera's battery charger. I thought a lot about building some sort of homemade charger, but just didn't dare try. Luckily it ran out on the very last day, but I'd like to know if it would've worked. Basically, the camera has a 7.4V Li-ion battery, which I'm guessing is just two cells/batteries connected in serial. Its charger is an external one, the camera itself has no power input. Afaik, a Li-ion battery's voltage is higher the more it is charged, and it's charged by just applying a higher voltage that "forces" current in the opposite direction. My idea was to connect two fully charged 3.7V Li-ion cell phone batteries in serial to make another "7.4V" battery, and then connect + to + and - to - between these two 7.4V batteries. The fully charged one should with its higher voltage slowly charge the discharged camera battery until their levels are about equal. Fully charge the phone batteries again and repeat if needed. This should never be able to charge the camera battery beyond 100%, so it should be safe. Would this have worked, and how safe would it be?