Just a word of warning to everyone, those screw heads are easily stripped if you aren’t careful…. I suspect they are done up by an electric scewdriver at the factory so they are gonna be tight… firstly make sure you use the right size scewdriver. (a nice snug fit, too big or too small and you are gonna have problems) In my experience it’s usually a little larger than you might imagine….. Don’t use an electric screwdriver and just gently put some pressure on the screws until they loosen… if the screwdriver slips in the head, use a different screwdriver size …. don’t keep trying until the head is damaged.

anyway…to the op, it would be best to get the battery out, but if it’s gonna be a lot of trouble I wouldn’t worry too much if you use a power supply there shouldn’t be any drain on the battery and big muffs don’t draw a lot of power anyway.. I’d imagine it would take literally years before the battery was in any danger of leaking.