Hmmm..... Interesting. Perhaps some of the older 4-in-1 units used lower voltage ESCs. I'm not sure, in that case it seems to be some 4-in-1s are 11.1v certified and some are not. Are you sure he wasn't flying a CX's 4-in-1?

Either way in light of this new info I'm upgrading my guide and am going to allocate the $70 I could spend on a new 4-in-1 for trying a 3 cell pack on a CellPro 4S LiPO Charger.