It could be that he is using something like a 1 ohm coil and the sigelei may only be a buck chip, not a buck/boost chip(not sure on buck or buck/boost, but I know my old sig 150 was only a buck chip). If that is the case, at 8.4v, it would only be able to put out 70.5 watts at a full charge, and keep going down as the batteries are being discharged.