LiPo Batteries – How to Charge and Discharge with BMS 3S

I've built several products around different chemistries. I have found LiPo the easiest to use since there are already specialised charger IC's that do all the work however, like you said, having them in series is not that straight forward. I believe the NiMH is a better solution if you don't have a lot of experience with chargers or if you don't find a good solution for charging LiPo in series.

Just one note, do not trickle charge NiMH indefinitely, use a timer at least to avoid overcharging the battery too much(even when you trickle them, they overcharge). You could also use, like Pwocky suggested, an LM317 to charge at a constant current and monitor the change in temperature in the battery pack, once the delta T becomes big enough (the temperature changes more rapidly) the battery is charged. You could also mix this method with delta V and a safety charge timer. This is what I do and it works perfectly. I charge my batteries fast and never overcharge them.

There is a lot of info online with graphs showing how the temperature changes when charging a NiMH battery.

If you haven't figured this out yet, series charging is accomplished by putting all the main power leads in series, and then putting the balance leads in series as well. The challenge is that each balance lead has an extra pin from the number of cells -- that's where the confusion comes in.

The first and last pins of the balance leads are directly connected to the first and last cells respectively, positive and ground. Think logically about how a fully-series pack is constructed, and where the balance taps are. They are between the positive and negative of each cell in series. Since your balance leads are broken out, you have one wire for a positive, and another wire for a negative.

Connect them together, and take the tap as one of the balance wires.