This is the casing for alternative version of
single micro:bit and purchase an extra 2xAAA Battery Holder with switch.

2xAAA Battery Holder with switch: https://my.cytron.io/p-2xaaa-battery-holder-with-on-off-switch
micro:bit Single: https://my.cytron.io/p-micro-bit-v2-mainboard
micro:bit Junior kit: https://my.cytron.io/p-micro-bit-junior-kit