I think lot of guys here on Instructables know how much satisfaction is obtained building a gadget entirely by ourselves, but... sometimes it could be a clever solution opting for some nice and ready accessory. I think this is one of these cases.
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.