Keyless Entry Transmitter
WARNING: This page is about a different car, the 2003 Saturn LW300, 2003 Saturn LW200, 2003 Saturn L300, and 2003 Saturn L200. However, it is still accessible from the selected car via links, so may be relevant.
The BCM will fail DTC B3109 - Keyless Entry Transmitter Low Battery when the transmitter battery voltage is below 2.5 volts. Nominal transmitter battery voltage is 3.0 volts.