Hi Dennis, welcome to the forum.
Check out this thread, it's one of many threads that has gone over charging the Mavic batteries in a vehicle.
This is one of the most recent I found doing a search.
Anyone else having problems charging ANY DJI batteries in the car? They don't want to charge unless the engine is RUNNING. Tried multiple car chargers, over 2 cars, one with a brand new car battery. Even tried a 12v/120v power inverter. Tried Mavic Air Batteries and now my new
Mavic Pro 2. No...
mavicpilots.com
My post #10 and subsequent follow ups describe one issue with the 12v DJI charger (voltage needs), and how to resolve it.
If you are driving, obviously the car alternator is keeping charge up to the battery, AND the charge rate will be more than enough to get the voltage needed, 13.1 - 14.0 for most vehicle alternators).
Once you stop a car, and the charging also stops, a battery will slowly drop voltage to settle around 12.7v, which isn't enough to properly run the larger Mavic chargers (my M1P and no doubt the M2).
Mine would kind of 'duty cycle' without the step converter, ~ 30 seconds on, 30 seconds off, never did charge a full battery I can recall, had to run the vehicle . . . usually ok when touring, but no good for camping.
A car battery in good condition, and of suitable capacity, should charge a couple of Mavic batteries without any concerns . . . maybe 3 or 4 are no issues either.
The
M2P battery is 3850 mAH, 3.85 Ah, a vehicle battery around 80 - 100 AH, so should be plenty of power for the car.
It needs that initial cranking power, so I wouldn't deplete the car battery by charging 6 or whatever batteries in one go, but the likelihood one would fly that many in one place is probably not going to happen with most pilots.
If you wanted to do that, just start the vehicle up and let it run for 20 mins after putting on say the third battery.
Most times people will fly a bit here, drive aways, fly another battery or two, etc etc.
I find the 12v car charger, is quite noticeably faster than using my 240v mains charger (with ample voltage supply), and it can use the same DJI 4 battery hub, charging a series of batteries consecutively as it does.