[suicideneil]

Is the pack that drains quicker always the same one, or just on the right side of the chassis (so it could be either lipo depending on which side you mount each one)?

Label them, run them, check them, charge them, then repaeat, only switching posistions to see if its the same lipo. Weird, but without some external influence they should stay very closely balanced- have you checked the balance tabs are clean so that the cells are being fully charged correctly, and there isnt a false reading on any of the cells cuased by dirt on the pins etc...