Good for you, another solution in our hobby. I like the Avistar, and am new enough, that I will likely have another and will try your approach when building that one. As to lateral balance you will find this far easier than your battery struggle. Some will glue a washer into the wing tip, or on the wing. I was able to get enough clear silicone into the plastic wingtip from the small open slot next to the aileron to balance out. Nothing cut, nothing shows, and since it is also an adhesive nothing moves.