a cr123a 3.0 volt is sufficient and easy to provide. the electric shutters of the the polaroids are quite robust, they would even work with a 9 volt battery without problems. I tested both for quite a while and they are both still working.
the easiest way imho is to purchase a cr123a pcb battery holder (google it). it's not even 1 dollar (+shipping of course) and fits into the battery compartment. attach the wires and that's it.
for the owners of those models with an electronic timer: you can easily fit two holders into the battery compartment.
greetings from the sunny south of france