Any suggestions to hold a rear mounted battery

[Carbon]

I use that heavy duty velcro on mine & it seems to work just fine. I'm not sure if it would stick to carpet but it sticks to wood damn good. Not sure on how good it would hold up if you were in an accident though so do it this way at your own risk.

Bad news for an accident///

[Deathflex]

Build a brace to hook with box