Small robots need small power sources, and this little 3.7V, 170mAh LiPoly unit from Seeed Studio is one of the smallest batteries we carry.
The manufacturer states that it can push up to 25C (4.25A) continuously, which is crazy! (Crazy cool or crazy dangerous, you decide). It is pre-wired with the standard 2-pin 2mm JST-PH connector, and has built-in protection against over voltage, over current, and minimum voltage.
Still, there is no substitute for good battery management, so try to treat all LiPoly cells gently, and best to recharge them slowly rather than at their maximum rate with a proper LiPoly charger.