NTT Docomo is developing a smart phone battery that can fully recharge in just 10 minutes. The major Japanese carrier (it has some 58 million Japanese customers) was showing off the device recently at CEATEC, an electronics exhibition in Japan, where a few reporters spotted it.

Details on the device, which is still in prototype, were scarce, but we have enough to get the general picture. Currently the battery takes the form of an external sleeve–not altogether unlike a Mophie “juice pack”–and only works for the time being with an Android phone, NEC’s Medias (which, while currently Japanese-specific, is supposedly coming to the US, someday).

How does NTT Docomo recharge the battery so quickly? Simply by cramming in more energy, faster. While a standard battery pulls something like 0.55 amps, NTT Docomo’s device pulls something like 5.85.

Everyone wants a faster-charging battery, of course, but NTT Docomo’s presentation raised as many questions as it answered. How does it cram so much energy into a battery so quickly without the battery growing terribly hot? And would the high-speed charging imply a shorter overall battery lifespan? (I’ve sent requests for comment to NTT Docomo, which hasn’t yet responded.) And don’t even ask for details on pricing, let alone release date–“as soon as possible,” was the only info NTT Docomo would give Engadget.

The question NTT Docomo seeks to answer–how do we get a faster-charging battery?–is more frequently asked of electric vehicles than of smart phones, since many analysts are convinced that EVs can only make inroads in markets once recharge times are comparable to refueling times. Quickening EV battery charges seems more crucial to me than speeding up smart phone charges–personally, my more typical problem is being caught without any outlet nearby at all when my iPhone’s battery kicks it. Once I do find an outlet, I’m rarely bothered by the charging time–if there’s an urgent smart-phone-necessitating matter at hand, I can typically achieve it while plugged in. Still, for folks who only have a short amount of time to dock before having to dash to the next location, such a battery would undoubtedly be a blessing.

While waiting for NTT Docomo to come to rescue, if you’re desperate for extended battery life–and like to disguise your gadgets as breath mints–try out one of my favorite accessories, Adafruit Industries’ “Minty Boost.” Twenty bucks buys you a battery pack that poses as an Altoids can; plug it in via USB to help your phone go the extra mile.