Our vehicle-powered devices report two voltage readings—one for the external voltage coming from the vehicle (eg. 12/24 volts) and the other for the internal backup battery (eg. ~4.2 volts when fully charged).

When the backup batteries on our other vehicle-powered devices are disconnected, the reported internal backup battery voltage is 0 V. However, on the Bolt2 due to a different charging circuit design, it would report 4.6+ volts.

Here's a summary of all the different states and typical voltages -