When the battery is fully charged and ready for use, the green LED turns on. There are two LEDs - one red and one green. Solder the backpack on with the extra long header so that it can still plug into a breadboard, or clip the long header leads short afterwards for a slim package. (Technically its overclocking but we've never seen that affect the microcontroller itself, AVRs are happy to overclock without complaint). However, many times, you can run a 5V microcontroller + accessories off of the ~4V from the LiPoly battery with no problem. Ideally, this backpack is for use with the 3.3V Pro Trinkets & ItsyBitsy, so that the battery voltage (3.7V-4.2V) will get regulated down to 3.3V on the board. Unplug the USB port and the microcontroller will switch over to the rechargeable battery. When the Pro Trinket or ItsyBitsy USB port is powered, the battery is recharged automatically.
This LiPoly backpack makes it really easy to do! Instead of wiring 2 or 3 boards together to make a charging system, this little PCB sits on top of the PCB and allows a LiPoly/LiIon battery to plug in. If you have an ItsyBitsy or Pro Trinket you probably know it's the perfect little size for a portable project.
