This battery holder connects 2 AAA batteries together in series for powering all kinds of projects. We spec'd these out because the box is nicely slim, and 2 AAA's add up to about 3V for low-voltage electronics projects, plus it has a nifty on-off switch. 

Fits any standard AAA battery. When using rechargeable NiMH the output voltage will range from about 2.7V with charged batteries to 1.8V at the end of life with a nominal voltage of 2.4V. When using alkalines, the output will range from 3.2V with new batteries to 2.2V at the end of life with a nominal voltage of about 3V.

The polarity matches that of our 2-pin JST cable and Li-Ion/Poly batteries. Uses a genuine JST connector so it won't 'catch and tear' in JST connectors.

This is a great update to the battery packs that come with micro:bit's because it has an on-off switch built in so you don't have to yank it out to turn off the power.