It's the Xiaomi battery brand.
If you run out of power, you can buy the official original battery or other brands of the same type of battery.
Xiaomi Mi Home smart door lock is a smart door lock officially released by Xiaomi on December 5, 2018, which supports 6 unlocking methods such as fingerprint password, and adopts C-level smart lock core configuration, which can be linked with Xiaomi smart devices.
The original battery of Xiaomi fingerprint lock is Xiaomi battery, and other brands of batteries can also be used.