5.2 Potentially Untinned Solder Pad Under the Coin Cell Battery Holder
In some cases, the PCB solder pad that enables contact with the positive side of the coin cell battery inside the BT1 connector is not tinned. As a result, electrical contact with the battery cannot be established, which prevents the device from receiving power from the coin cell.
Work Around
Tin the solder pad, or connect an external battery using the J4 header, or contact your Microchip Sales representative.