For 1990-2009 cars
Battery 1: The scan tool displays 0-20 Volts. The scan tool displays the voltage as received on the battery positive voltage circuit of the BCM.
Generator L-Terminal: The scan tool displays On/Off. The scan tool displays Off until the engine is running, then the ECM supplies then the percentage value varies depending on electrical loads
Ignition 1: The scan tool displays 0-20 Volts. The scan tool displays the voltage as received on the Ignition 1 circuit to the ECM.