Winfried, this year Chad and I discovered what may be the simplest and most minimal battery mount. The two packs are held together with outer strapping of velcro or tape. The pair of packs has two small pieces of velcro on the outside surface that mates with two small strips of velcro on the mounting plate (permanently installed). Two outer straps of velcro hold the packs down against the plate. This allows lots of freedom to set the packs forward or backward to adjust CofG, but holds them firmly in position once strapped in.

For our Twisters we are going to add a second landing gear brace in front of the real one. Then a wood plate is set and glued on top of those braces, that spans the area between them. The plate will have strips of velcro, the packs will have strips of velcro, and there will be two velcro straps around the plate and pack to hold it down.