I'm not sure this is right. Anecdotally, I have 3 different Piezo systems (2 by KK Sound, one by Shadow) which do not require power and which generate enough signal to be heard when plugged into a random amp. They do all sound better with a high impedance it is true, so I would guess the battery is there to power the preamp and isn't required for the piezo.
The problem sounds like a short to me, either the socket is broken or the wiring has a fault.