I’ve built at least two dozen MintyBoosts – some with 4 x AA alkalines, some with rechargeable 2 x A123 NiCads, and of course the standard 2 x AA – and finally decided to build a rechargeable version. I’ve long had the idea, but wasn’t too keen after doing a bit of research on lithium polymer batteries and what is truly meant by “vents with flame” (see this and this, for just a couple of examples). I finally got over the fear and built two in a single morning. I used LadyAda’s MintyBoost circuit board, SparkFun’s LiPo charger, and a couple of the dozens of mint containers I have sitting about. The larger tin contains a 2200 mAh battery I got from RapidRepair for a measly 6 bucks (purchased 3, actually) while the smaller uses an iRiver Clix 720 mAh battery I got from BatteryShip (and cost more than 3x more than the 2200, though it did come with a nice set of minature tools).
My SparkFun charger is an older version of the one depicted at the link above, the only difference being that mine didn’t have the JST (?) connectors. I had originally purchased and planned to use SparkFun’s 2000 mAh battery and decided on a layout which required a bit of modification to both the battery and the charger such that everything could be attached to the bottom of the tin – no mounting of components on top of the battery. When the 2200 mAh iPod batteries arrived, I was pleased to discover that they were perfectly suited the task, but because it was larger I’d have to place the recharging and boost circuitry on top of the battery. Not a problem, really, as for a number of years I made a living installing Nortel and Alcatel SONET equipment and have a roll or two of fish paper electrical insulation left over. I cut the fish paper to size, used spray-on adhesive to glue it to the battery, hot glued the battery into the tin, then aligned and hot glued the circuit boards to the fish paper.
The mini Penguin was a bit different. I had to desolder the DC barrel jack from the board and cut as much off of the board behind the connector solder pads as was possible. I didn’t modify the boost circuit board, but when I do another one I’ll do a bit of reconfiguration to avoid having to cut a hole in the lid. I think next time I’ll eliminate the 8-pin socket and solder the uC directly to the board to get it out of the way – it *barely* closes as it is. I also need to find a shorter inductor. I’ve pulled parts from tons of old electronics boards, but have yet to find a suitable part, probably an SMT (surface mount) part. And while I’m at it, replace everything I can with SMT. Heck, it might even get to the point where I actually make my own boards designed specifically to use SMTs.
In testing, the larger unit recharged my Android Dev 1 with no problem. Hardly a dent in the 2200 mAh battery. However, the Lil Penguin didn’t fair so well. It took my Dev 1 to only about 65%. That isn’t bad, though, and it’ll do in a pinch. The key here is that the device is only for emergency use and it’s tiny, so I’m driven to improve the design.