Although fuel cells aren't yet at the point where they can fit easily into devices like the Zune, the iPod, or cellphones, they are small enough to be used as rechargers. This is why Medis Technologies has produced the first of its Microsoft-branded fuel cell rechargers, and should be up to a capacity of 1 million units per month by the end of June.
Neither company is saying what the rechargers are for, but if you take a look at Microsoft's line of portable gadgets, there aren't a whole lot that really call for recharging on the go. That leaves the Zune, the next-gen Zune, and the Zune Phone. If we had to guess, we'd say making sure you can make a phone call after a midnight rest stop hookup goes awry weighs a bit higher than making sure you can continue air-guitaring Woman by Wolfmother.