This is a unique two-cell AA battery holder. The 6" (~150mm) cable has been terminated with a JST-PH connector.
We used to recommend using this battery pack with the BBC micro:bit but due to inconsistent JST connector sizes from our supplier (just enough for it to get stuck), we no longer do. If you are looking for a battery pack that is a bit easier to plug and unplug from your micro:bit, we recommend picking up the AAA-sized version instead!
Note: Please keep in mind that JST connectors are not suited for constant and repeated removal and insertions and may wear out over time.