I power the RoboCupJr robot with a Turnigy nano-tech 2200mAh 2 cell Li-Po.
I use a V7805-2000 switching regulator (recommended by Steven Kibler) to supply power to the BeagleBone Black. A 10μF/25V capacitor is connected between the Vin and GND pins and a 22μF/16V capacitor is connected between the Vout and GND pins as described in the V7805-2000's data sheet. For overcurrent protection, I added a 1.85A PTC resettable fuse. For reverse polarity protection, I added a P-Channel MOSFET as described in Afrotechmod's YouTube Video on How to protect circuits from reversed voltage polarity!