Some people have brought up very valid concerns about battery expansion in this project. I'm working with some ideas on how to easily add an external battery rather than keeping it inside the block of epoxy, so I'd suggest doing something similar if you want to build a project like this yourself.

The epoxy is about an order of magnitude more thermally conductive than air (meaning heat dissipation is not really a problem -- the unit will stay cooler than it would outside of the epoxy due to the greater surface area of the block) but there could still be some potential outgassing issues. So if you build this, do your own research and thinking about the battery.