This is an open battery holder for 2x AA batteries with 2 pin PH connector with 2.0mm pitch. The connector is the right type and polarity for powering BBC micro:bit board. AA batteries hold more juice compared to AAA batteries used in most micro:bit kits.

If you want to use it for other boards, Pay attention to the polarity of the connector (red for positive, black for ground). You might need to swap the wire position on the connector which can be done easily using a pair of tweezers.