The following DIY manual describes an easy-to-implement battery backup module for the BeagleBone Black. This can be useful in certain applications, such as out-door usage where constant power is not present and it is not desirable to just drop power on the BBB board. It was built for a RasPBX setup with the motivation to have a safely powered BBB in all situations. The BBB is unfortunately suceptible to slowly rising supply voltage when powered on. It sometimes does not boot at all, which can be a serious problem after a power glitch. On top, voltage irregularities can cause the device to crash as well.

The battery backup can be applied to any BBB installation, running RasPBX, the original Anstrom Linux or any other distribution. However, USB devices cannot be used while running on battery, as the UPS does not power the USB host port.

Full article here:
Uninterruptible Power Supply (UPS) for BeagleBone Black – a DIY Project