PiJuice — Uninterruptable Power Supply for Raspberry Pi
Using the PiJuice from PiSupply you can use your Raspberry Pi without a mains power adapter. Or for a while anyway. It has been designed as a UPS (Uninterruptable Power Supply) and can ride through several hours. The PiJuice is configured as a HAT for the Raspberry Pi and plugs without any problems onto the 40-pin RPi header.