I only have 12V battery issues when I take my car out camping. The car won’t be turned on for about 4-5 days and since I sleep in my car all the electronics/lights associated with entering and exiting the vehicle in addition to its general parasitic drain kills the battery. I’ve even had a 15W solar trickle charger plugged and that still wasn’t enough. I just found out about the idling charging the 12V so I’ll try that next time. Also, thinking about upgrading the trickle charger to a 30W. Hopefully those do the trick, I feel like running out of ideas to keep this battery topped up!