
Charlie Brett's suggestion -- buy one of the disposable flash cameras, use
the film, then take the thing apart -- is a good one.  Note, though, that
you won't get a particularly precise voltage out of such a thing, and it
may be a single-point design that won't adapt well to off-nominal operation.

The things are easy to dismantle.  The key piece of information is that
when you advance the film on one of them, you are winding it *into* the
film cassette -- it is unwound from the cassette in the factory, when
the camera is made.  So no darkroom is needed for dismantling.  It's
standard film, so just take the cassette in for processing.

All the camera-store people do when you bring in one of the disposables
is rip it apart, toss the film cassette into the to-be-processed bin,
and throw the battery in one trashcan and the rest of the camera in
another.  If you take it apart yourself, you get an AA alkaline battery
(still with a fair bit of life in it) and all kinds of little bits and
pieces from the camera.

I expect you could even re-load and re-use the camera if you were really
determined.