[jhautz]

Seems to me the most popular lipo sizes out there are the enerland size cells and the Max Amps size cells which are both 45-46mm wide. If you made it fit a 166 mm long battery it would fit the enerland based 5000mah packs and the Maxamps 5000 packs. (as welss many other of the pack sizes) The maxamps are a little shorter and thicker but it would still work.

Another possibility would be to have the back of the battery tray be a separate piece that could be adjustbale for the battery lengeth and held inplace with the screw that holds the strap down.