This is a dummy battery for the Canon IXUS/SD series of digital cameras (Battery NB-4L). This was just a test to see if my initial design would fit into the camera, after some minor sanding on the edges it fits perfectly.
I plan on making some further modifications to add conductors for the battery terminals which will allow me to hook the camera up to a DC supply (there is a flap on the battery door for a cable to go through). Canon do actually sell a product that does exactly this but as you can imagine it costs a fortune. I had a quick look on eBay and the cheapest one was about two times the amount I paid for the camera.
This camera and many other Canons in this series support CHDK which is custom firmware that allows you to do some cool stuff like time-lapse and remote triggering. You soon run out of juice on a single battery which is why a DC supply is essential for any kind of real hacking.
This is part of a much bigger project which will follow up on Schmarty's work and involves some software mods to ReplicatorG and the Thing-O-Matic motherboard firmware.
Please let me know if you have any input on how I could go about adding conductors. I think I will need to hollow out the design to allow for connections, I was thinking something like nails for the conductors, inserted into the top and then solder wires to the end of the nails.