The Raspberry Pi is small and doesn't consume a lot of power, but it lacks portability. If you're looking for a lot of juice on-the-go, Make shows you how to convert an old battery pack from a cordless drill to power the Raspberry Pi.
A drill battery obviously bulks of the Raspberry Pi quite a bit, but it does do the job of providing long-lasting power. It takes a bit of technical know-how to convert the battery to plug into the Pi without causing a fire, but once it's done you'll have a portable, rechargeable and long-lasting battery for your Pi. Head over to Make for the full guide.