One thing to keep in mind about these packs is that they are wide. I bought 2 of the ZIPPY-H 4000mAh 4S1P 25-35C Lipoly Packs, they say they are 50mm wide. I measure 51.5mm wide. They don't fit any of my battery compartments right now. Kind of a pain. So I will have to modify my cars or sell the packs.