DTC U2109-91: Back-up Battery - Parametric: Action

NOTE: The vehicle engine MUST be running to charge the telematic back-up battery. Ignition On will NOT recharge the telematic back-up battery

Refer to the relevant article of the service information and check the startup battery condition. If the startup battery charge is low, recharge/replace the startup battery as necessary
Run the vehicle for a minimum of 60 minutes to charge the TCU back-up battery
Check the telematic back-up battery voltage. A charged battery will show above 3.3V
Using the Jaguar Land Rover approved diagnostic equipment, clear the DTCs and wait 10 seconds
Read DTCs and make sure no warning message is visible on the Instrument Cluster (IC)