Untill the instructs say its ok to use more than 6 volts i'm going to stay with the 4 cell packs, at the moment I'm useing a 1400 MA 4 cell that holds up great I made myself from ni-cads batterys. I run the plane on A123's and I can't see what the big deal is if they don't match the Ign batteries unless you try to charge them with the wrong settings, but I take my batteries out before I charge so I doubt that will happen. I had a new 1800MA 5 cell Ni-MI pack that I wanted to use in this last plane but I wasn't to sure when I saw the 4.8-6 volts on the side of the Ign box.,also the instructions says not to run over 6 volts.  Like Jody said a 5 cell can go way over 6 volts at full charge so why take a chance on letting the smoke out of a good working ign box.</p>