It was bound to happen, with everyone making docks for their devices out of LEGO® bricks, it only makes sense that someone would mold a platform for LEGO&bricks around a battery. You could of course build a box around one you already own but this streamlined buildable battery I saw on CNET is a good way to go if you don’t have a battery already. I’m not certain its officially licensed, the power brick itself lacks the LEGO logo on it’s studs but the bricks it comes with appear to be official. The shopping page appears to have honored The LEGO Company’s fair use guidelines and even uses the logo, though not on the package of the power brick itself as far as I can see. .