For FingerTec i-Kiosk 100 Plus, Face ID 2, and TA300 terminals, despite the power adaptor being the major power supplier, these models are designed with built-in backup battery to prolong the usage of the terminals for another 2-4 hours when power failure. The Lithium backup battery is same as your cellphone/smartphone battery, which is easily recharged while the terminals are running on the main power source.