Powering headlights by plugging in

Does anyone know if it is possible to use the headlights with the car plugged in without draining the 12V battery? There isn't a 12V battery charge indicator, so I don't have a way to know if the battery is being drained other than trying it and seeing if the car still starts. I sometimes need a light in my driveway and using the PIP headlights would be easier than dragging out a work light. I think it works if the car is left on, but I'm not sure.

 

I couldn't find anything in the faq, so I checked with a voltmeter. While the car is charging, the 12V battery is at 14.5V. When plugged in after the charge is done, the 12V battery is at about 12.5V. When the car is on in accessory mode (and not charging, whether plugged in or not), the 12V battery is at 12.5V. When the car is on and the display says "ready", the 12V battery is at 14.5V.

This means that the 12V battery is charged while the car is charging or in ready mode, but not while in accessory mode. The car cannot be in ready mode while the plug is attached. So the headlights can be left on without draining the 12V battery while the car is charging or while it is unplugged and fully on. In the second case, the miles remaining indicator decreases as the hybrid battery drains. I didn't pay attention to how fast it was going down, but someone interested in knowing how much range you lose with the headlights on could use this method to find out.

This turns out to not be useful for me, because my goal was not needing to unplug the car to plug in a work light (I only have one outdoor outlet that can handle the current draw of either). But the hybrid battery charges even with the headlights on, and once it is fully charged, the headlights will be powered by the 12V battery until it is dead (and I doubt that would take very long).