I'm using a Futaba (Sanyo) 250maH NiCd battery. Here's a quick picture of my hatch. I've gotta run at the moment but it at least shows it's location (let me know if you need more info). It's made of 1/64 ply and I just covered it with some blue I had lying around. Later on if I get a color match I'll redo it in that wonderful purple/pink color . It's pretty much the same as was shown in earlier posts, just in a different location. Those are small servo screws holding it in and the battery is velcro-ed to the bottom of the wing (with one extra thickness of balsa sheeting for strength). It balances just past 4". My receiver is in the nose, under the engine tray right up against the wing's leading edge...nothing special there.

Chuck