Polymer Li-Ion Single Cell Battery 3.7V 30mAh 10*10*4mm

From the shop's description

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 30mAh & Dimentions 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