The Mugen Power Battery Case consists of a built-in Li Polymer batter, voltage 3.7v and a capacity of (mAh) 1500. It is available in brown or blue and comes with the USB to micro usb charging lead.
Mugen do a range of add-on batteries and travel cases to power your devices. You can use them either as a spare battery to give yourself extra battery life on a long day or you can use them as a complete replacement battery to give yourself the extended life without adding extra to your gadget load. In addition, there are available slip-on cases.