This adapter can be slid into a side-insert CR2032 coin cell battery holder and replace a coin cell battery. Plug in a 5V source to the USB-C connector, the power source must come from a USB-A receptacle, it will not work with USB-C to USB-C cables. There is an on-board voltage converter that converts USB power to 3V which is typical of a coin cell. You can select between outputting 5V and 3V on the coin cell adapter pads, 5V can be useful for devices that use two stacked CR2016 batteries to provide 5-6V. NOTE THAT SELECTING 5V OUTPUT CAN DAMAGE 3V DEVICES. There is an ON/OFF switch which connects and disconnects power to the coin cell adapter pads. There are also 2 JST-PH 2-pin connectors that can be used with the included cable to daisy-chain multiples of these boards together so you can power several devices off of a single USB source.