Been doing this for years with my Guild F4CE-NT electric acoustic, Bruce. I have to take off almost all my strings to gain access to the battery for the onboard preamp. I learned the capo trick early, though I clamp it on further up the neck, around the 10th fret or so.

And have been cursing whoever designed that guitar ever since, because they also designed it with one of those stupid little oval soundholes that makes it that much harder to get your hand inside and up to where the battery is held in that little spring-steel clip. Lots of fun trying to do that between sets. So now I change my battery more often than I need to probably since I don't want to get caught out. And no, phantom power on the board does not prevent battery drain; as soon as you plug the guitar in, the battery is on and being drawn from.

It also causes me to look at my buddy's Tak with its easy-access battery compartment and wonder if it's worth compromising my "lifetime warranty" by installing something like it on my "working guitar".