So I did not want to spend the money on the Blue ROV battery, and I was wondering, if I could encase the leads on a SLA battery (Link to battery) with epoxy, and expose it to high pressure under water. (9.81 bar/ 9.68 atm) Would this damage the battery?
The biggest issue is the case itself. The next in-line is going to be how pressure / watertight your fittings going to the post are.
If you wanted to build a case for the battery, that is a different story. You would need to have pressure proof penetrations for your power lines but it is totally possible.
You would also need more bouyancy.