Fortunately, single-chip solutions are now widely available for Li-Po battery charging. The tiny chip TP4056/YP4056 is a good example. The TP4056 IC is a complete constant current/constant-voltage ...

I made this amazing battery pack using 18650 cells, performing about 3X better than a LiPo battery of roughly the same weight and size. So instead of flying for 15 min, now you can fly for 45 min.