This is something I have been working on for some time as one of my first projects, it's basically a Car Battery that you can hook up on the back of your Power Armor with wires going into the Fusion Core slot, the dream moving forward would be having this as an item you can find and use instead of just a Retexture, having it as a limited power source. I might do this at some point when i learn more about the modding tools.

This would still be lore friendly as lead acid batteries are already around in the fallout universe.