This battery holder connects 3 AAA batteries together in series for powering all kinds of projects. We spec'd these out because the box is slim, and 3 AAA's add up to about 3.3-4.5V, a very similar range to Lithium Ion/polymer (Li-Ion) batteries and have an on-off switch. That makes them ideal for use with 3.3V projects that have a 2-pin JST connector meant for one of our Li-Ion/Poly batteries. (Of course, you can't recharge them like Li-Ion/Polys, so don't try to plug this into one of our Li-Ion/Poly charger boards!) Fits any standard AAA battery. When using rechargeable NiMH the output voltage will range from about 3.7V with charged batteries to 2.7V at the end of life with a nominal voltage of 3.6V. When using alkalines, the output will range from 4.6V with new batteries to 3.3V at the end of life with a nominal voltage of about 4.5V The polarity matches that of our 2-pin JST cable and Li-Ion/Poly batteries. Uses a genuine JST connector so it wont 'catch and tear' in JST conne