I converted my Vibirus tricycle to support a higher torque motor to help it climb hills. A 48v battery I bought was 26mm shorter than the stock battery so I made this riser. The battery also connects with a connector at the bottom so there's a spot for that and to snake the wire out of the side.

If you need it longer or shorter, the Fusion 360 model is there or you can scale the stl file

You'll need 4x 10-32 2" screws. They'll poke thru the bottom a bit but that's ok.