Do you mean: Charging AA, using it one hour, then SHUTTING IT DOWN, waiting 4 days and then turning it on? If that is the case, then I always get a good 22 hours out my dual batteries regardless of the number of times I turn it off.
HOWEVER, if you leave it on but just not playing music, the Raspberry Pi is a full blown computer. It will consume battery life quite a bit.
It would be nice if you could be a little more precise in your example so we could compare more accurately with our own observations.
