Polymer Li-Ion Single Cell Battery 3.7V 50mAh 20*10*4mm 401020 2 wire

From the shop's description

Polymer Li-Ion Single Cell Battery 3.7V 50mAh 20*10*4mm 401020 2 wire These are very slim, extremely light weight batteries based on the new Polymer Lithium Ion chemistry. This is the highest energy density currently in production. Each cells outputs a nominal 3.7V at 50mAh & Dimensions 20*10*4mm These batteries require special charging. Do not attempt to charge these with anything but a specialized LiPo charger. Battery includes built-in protection against over voltage, over current, and minimum voltage