My grandson (7 years old) and I been running my old rc’s for a bit (Savage X 4.6, TMaxx 3.3, Slash 4x4 w/7 cell, etc). He’s pretty capable at controlling and bashing them. I’m getting him a Vorteks 3S 4x4 and was wondering if I should go with 2S or 3S batteries as I’m not that familiar with the lipos.