Effects Pedal Battery Explodes--when Unit is off

Car batteries can develop shorts internally when getting ready to go to little battery grave-yards. I saw the results of a couple of them doing that in certain minivans's OE units back in the mid-90's. Nasty messes. I wonder if widdle 9 volters can do the same?

those shorted car battery plates are being driven by the alternator/regulator that's attempting to charge the battery. nasty. not really the same situation for the lil 9 volts.