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 350mAh & Dimentions 40x20x4 mm (Length x Width x Thickness)
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.
The battery photo in not same as real shape - the photo is just for reference - check the battery dimensions for actual size