Mine are absolutely consistent - the bec side is down 400-700mah from the other batt over a 15-17min run. When I was running NiMHs (7 cells packs, so they were "handed"), I used to wonder why the left one would always take 500-900mah more when re-charged. My lipos show a little bit less diff.

If his lipo experienced a prob, that would explain things and make sense.