My 3906 runs the orig red EVX and have run pair of 2S lipos with no trouble. I either run twin 7 cell NiMh packs of pair of 5000mah 2S lipos. I use a fan on the esc.

The 7 cell packs actually have higher voltage than 2S lipos initially - 9.8 - 9.9v, so that's 19.6v+ and mine has never had an issue running with it.