The AmpKing 20700 battery is a perfect choice.  It won’t break the bank, has been tested and offers all the power you could ask for.

3000mAh capacity coupled with a continuous discharge current of 35 amps make the AmpKing 20700 mod battery a top contender!

Size – 20mm x 70mm
Nominal voltage – 3.70V
Nominal capacity – 3000mAh
Continuous discharge current – 35A
Max charge current – 4A