GunfighterII

To charge each cell individually, (balancing charge), you would have to bring out a separate wire from the + side of each cell and a ground wire that is common to all cells. To charge a 5s Lipo as a pack, using only two wires and a +12V source, you would need a charger that looks something like the attachment below.

1. The 12V DC in can come from a battery or a computer power supply.
2. The first stage is an inverter circuit that converts 12V DC to 12V AC.
3. The 12V AC is input to a 1:3 step up transformer that will have an output of approximately 36V RMS.
4. This is rectified and filtered to provide approximately 40V DC to the regulator circuit.
5. The regulators will get their control voltages from the D/A ports of the microprocessor and you will have a charger that can deliver up to 35V DC and is current limited to whatever current is selected.

However, if you intended to charge a 5s pack up to 21V at a 1 amp rate that would be a 21 watt load. A charger is only going to be about 75% efficient so the source supply would have to be capable of sourcing about 28.5 watts. On a 12V supply it would have to source about 2.4 amps.