This battery holder is by far the easiest way to add a battery to a small wearable project. By coincidence, there are two small 1mm diameter holes in the metal connection tabs, just large enough for a #5 or smaller needle to pass through. One tab connects to common ground (negative) and the other tab is +3 Volts.This holder is meant to be used with Lithium CR2032 (20mm diameter, 3.2mm thick) sized coin batteries. These are almost always 3V at about 200+ mAh capacity. Lithium coin cells are not rechargeable but they are very easy to find, available at any grocery store.