6S 2500 mAh will do the task, unless you have a very inefficient gearing.
Maybe that you can get away with 2200 mAh.
We can in Hannibalito 4. That uses a set of Gimson GR01's and 170mm wheel controlled by a Scorpion XL Ilyama version, and the battery is a 3S 2200mAh. Never pulled out more than 1400mAh in a full fight. Typical it is 700-800 mAh.