Inspired by a recent post on a facebook group, I decided to give this a try, using the cell from a solar powered calculator. I tracked down a suitable donor calculator online, and ordered 5 - they were $1 each (50p in your money). They are simple to dismantle, to remove the solar cell, which isn't soldered in - the connections are glued to the cell. I soldered leads to the cell, and tested the output with a voltmeter. The cell was taller than the original, but not as wide, so I modified the bezel, and put a piece of black card either side. A piece of electrical tape across the back holds everything together, and the bezel fits normally in the camera top plate. The new cell wired to the meter - I put a 4k7 resistor in series with the cell.