The battery backup system backs up the RTC of the XMEGA. It consists of a coin cell battery, a battery holder and a jumper that can be used to disconnect the battery from the Xmega. A manganese dioxide lithium battery (CR1220) from Panasonic with a nominal voltage of 3V and nominal capacity of 35 mAh is used in this design. In order measure the backup system power consumption the jumper from the header can be removed and replaced by a current measurement probe. The header is shown in the section "Kit overview" and is also marked with “VBAT” on the PCB silkscreen. The jumper can also be used to simulate battery insertion and removal without actually removing the battery from the holder.