I'm thinking M12 battery or M18 battery and a step-down converter hooked to the camera. I'd like to be able to have the battery connected right onto the camera or inside it if I could make the M12 work.
I emailed a camera company asking them in the future to consider a camera that would use M12 or M18 batteries.
We'll see if I get anywhere with them.
I don't like the idea of external items like solar, wires batteries that bears could easily get into.