The kit requires a 7.2V 6-cell flat battery pack with standard Tamiya connector. Capacity varies between different packs, so you decide on what capacity to get.

The running time depends on the capacity of the battery (mAh). The higher the capacity rating in milli amps, the longer the run time.

There are many good 7.2V battery packs on the market. Take your pick. Usually you get what you pay for.