According to a teardown of this device posted on youtube by mikeselectricstuff there are two curved lipo cells soldered in place in this device. You need to exercise care when working with lipo batteries so you dont accidentaly short them out. Perhaps you could try ebay and see if you can find the right type of curved cell there. Bending a normal lipo cell into the reqiured curve is not something you should try as this could make the cell prone to exploding/cathing on fire.