Yep, I'm putting a larger engine on my UltraStick 40 and will be moving the battery pack to the rear of the fuze by cutting a trap door in the bottom of the fuze. I try not to add any weights until all components have been moved as far as they will go. As Colin Chapman, founder of Lotus always preached, Add Lightness

Trading out the TT GP42 for and Aviastar 53 moves the battery pack backwards about 6-8 inches.

The H9 manual is pretty good for balancing info. Follow it and the plane will be fine. The US has a pretty wide range of acceptable balance points, I seem to recall that it's about 1/2 inch wide area and right around the spar.

Jack