This tiny board has a standard DC barrel jack socket at one end and provides a regulated 3.3V output that you can use to power your micro:bit using the JST battery connector attached to wires coming from the other end of the board.
You can use the power board if you want to use a AC to DC adapter (6V recommended), solar panels, or other sources of power that are not the 3V or so that the micro:bit is expecting. The Power for micro:bit will accept an input voltage of 4.5 to 12V DC from its standard DC barrel jack socket and convert it into a pleasantly regulated 3.3V for your micro:bit.
The micro:bit’s battery connector is connected directly to the 3V alligator clip-able connector of the micro:bit, you can supply other things that are connected to the micro:bit with a lot more than the allowed 90mA. In fact you can supply up to 700mA. This makes the board great for use with things like NeoPixel strips or servomotors that need a bit more current.
Works with micro:bit V1 & V2