The revo is made to run on a 4S set up. One 2S or 2 cell pack per side. They are then wired in series to create a 4S pack or the esc will have two separate plugs on it one for each pack. A 2S2P pack is still a 2S or 2 cell pack. It's just made up of two groups of two smaller cell capacities to make a larger capacity pack.

Jason