+ socket in the engine compartment

Hello, everybody.
Does anyone know if the + connection in the engine compartment permanently delivers 12V or shuts down? I have built a warm-up heater from Waeco that also charges the battery overnight. I just connected the device to this + socket and the control panel in the interior is also supplied with 12V if the 220V plug is not connected. Unfortunately, the control panel loses the system data over time, so 12V must be gone.

Greetings from the Allgäu, Heiko