How does your submission match the theme?
There are multiple elements which serve more than one purpose, but I focused on giving the battery multiple purposes.

The battery serves as your hit points and as the resource for your special move. It also makes it a bit difficult to gain points, as those are just rewarded if you kill enemies with a fully charged battery. In my early designs it meant game over, if your battery was empty, but this wasn’t fun at all so I removed this feature.

Third-party resources
Unity

Contributors
Just me, R.Tedz