LEGO’s Power Functions elements mostly consist of DC motors and the hardware to be driven by those motors like gears and wheels. They also include battery packs, usually a bunch of AA cells in a plastic box. One of the challenges of the system — for hackers, anyway — is interfacing with the product line’s plugs, which resemble 2×2 plates with power and ground connectors built in, designed to be impossible to connect in reverse. It’s difficult to make the physical shape of the plug, with the connectors right where they should be. This hurdle means you also pretty much have to use LEGO’s power boxes or take your chances with frying your components from an unregulated LiPo.
The LiPo Power Brick project serves as a DC-DC power supply, serving up constant 9 V output, with
over current protection limiting current to 3 A peak or 2 A continuous and over-discharge protection shutting down the power supply when it zeroes out. It can be used in conjunction with Sbrick smart Power Functions controllers. The SBrick can also source 3A per channel, which is more than any LEGO PF-compatible power supply can deliver.
The LiPo Power Brick is the same size as a standard 2×4 brick, allowing you to easily add it to your next project.