I wanted to build the ring light the guy over at Metku.net put together, but I knew I didn't want to get bogged down by a wire tethered to an outlet. I've a 12v battery from a drill, but needless to say, it's bulky and unattractive, so I did some digging on 12v batteries and found the small A23 battery size apparently used in remote car door openers.
The A23 size is small enough to fit into many of the smaller mint tins and still leave enough room for a switch. There's a few commercial battery holders for this size of battery, but it occurred to me that the batteries already fit very nicely in the packaging. I mean, of course it does; if it didn't, it'd be pretty lousy packaging.
The obvious thing to do here was to take the packaging, add the needed contacts to it and stick it all in an Altoids tin I kept around for just such an occasion.
For the electrical contacts, I pulled the spring contacts from the board of a CD player that had gotten broken years ago, and clipped them down to an appropriate size. The little nub gives me a nice surface for the negative terminal on the batteries.
I wanted to have something a little springy behind the electical contacts to help make a firm connection, so I adhered the electrical contacts with a bit of foamy double sided tape. Slip the batteries in and we've got a custom battery pack for atypical batteries.
Turning the battery pack into a polished end-product is a pretty vanilla affair that I imagine we've all seen before. The short version is that I gave my custom battery pack a duct-tape wrap around the outside of the shell to help deal with the added stress. I then trimmed the excess plastic from around the top and attached the trimmed-down, taped-up pack to the inside of the tin with double sided tape.
The only interesting part of the end product is that I used a section of the rubber used to absorb vibrations in the CD player to line the edge of the hole that provides access to the power plug. This is to prevent the wire casing from becoming worn against the bare metal edge and to give the end product a cleaner look.
The photo captures it poorly, but these little batteries push the LEDs very nicely.