Car won’t start without a jump

I have a 2011 Prius that won’t start without a jump.

I work on a remote island at the moment and my car is parked on a more populated island. Every two weeks I’ve gone over, started it up, and driven it around a bit just to keep it from sitting too long. Been doing this for 3 months. But this time it wouldn’t start. Got a jump, drove okay, but when I turned it off everything died immediately. All lights, dash etc. Got another jump, drove again, this time for an hour. Same problem when I stopped.

The battery is new, replaced in December 2024.

There’s a ton of mouse and rat droppings everywhere. Is it possible they chewed through something important? Is it more likely the battery? Where do I start looking?