I recently had the need to have a power supply for my Canon DSLR, an EOS 40D, to make some timelapse. For this pourpose I've bought an LM2596S step-down adjustable power supply module from eBay, it's very cheap, efficient, compact, and (I hope) safe... and it fits exactly inside my exhausted lithium battery case. And this instructable could be handy adapted for almost any digital camera battery, the only requirement is that the case contains the power supply module.
Step 1: Intro
Step 2: What's inside?
You have to cut/crack the plastic casing all around the perimeter, because it's glued verty sturdy. Inside you'll find two 18490 Li-ion batteries, which are very rare to find to replace.
Step 3: Keep the shells
Maybe you wish to keep the protection circuit as replacement...