[Black Pearl UK]

Is the radio on its own fuse? I'd be popping that out first to see if it cuts the power.

 

[Black Pearl UK]

OK, bit more info needed.

How much is the drain? If you were to leave the car overnight, would it start the next day or does it randomly struggle to start every now and then etc?

Have you considered the thought of a booster battery pack so you don't get stranded in the middle of nowhere?