Hi Syman,
The American ThunderPower PL (Pro-Lite) Lithium Polymer packs have been around for a while now and are very well respected in the field that they were developed for, that of model flying.
The latest generation packs are advertised as having a continuous current output capability of 18C (18 x the capacity of the pack). In the case of the pack you are suggesting (6Ah) that would allow a continuous discharge current of 108A, well above the requirement of your bike (I hope, LOL!).
The packs come without any BMS (battery management system), this is all carefully taken care of with the manufacturers charger via individual cell balancing connections and with our electronic motor speed controllers which prevent over discharging the cells.
Pete.