So you're saying I should situate them vertically, side by side (as opposed to stacking them) in the bottom center of the plane, right? Also - how do you suggest velcroing them? Maybe have some velcro that goes between the two of them to keep them together, and then maybe some velcro on the bottom? Only problem is that they will be about a quarter of an inch above the bottom of the plane due to the frame (I was thinking I'd have them lying on the frame). Thus there won't be much of anywhere to stick them on the bottom... Any suggestions? Oh - I should metnion the fronts of the batteries will be up against the firewall, but I have not entirely decided how to hold the backs of them - I was thinking I'd probabaly put a fairly thick piece of balsa going across the backs of them with a piece of foam between the batteries and the balsa, but I'll have to figure out some way to do that so that the batteries can still be removed...