DTC U2109-09: Back-up Battery - Component failures: Action

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2018 Land Rover Range Rover, 2017 Land Rover Range Rover, 2016 Land Rover Range Rover, 2015 Land Rover Range Rover, and 2014 Land Rover Range Rover. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Following an emergency call or stolen vehicle tracking alert, a new telematics control module internal battery must be installed before this DTC can be cleared

Check backup battery for poor connection or not connected
Refer to the appropriate system wiring diagrams and check the telematics control module internal battery circuit for open circuit, high resistance
Using JLR approved diagnostic equipment, clear the DTCs and perform routine - Test Internal Backup Battery (0x040C). If the fault persists, install a new telematics control module internal battery. Using JLR approved diagnostic equipment, reset the non rechargeable battery power level following the backup battery replacement process