[Motorola] Vehicle battery chargers for EX-500?

[Coote, Jay]

I may be looking for ways to charge EX-500 handhelds or their batteries
in the trunks of vehicles.  Motorola, or no one seems to have anything.
The single-unit desk charger wall-wart power supplies are 18-19V no
load, so I'm not sure that putting one of these chargers on 14V vehicle
ignition power would work.  Has anyone been there and done that?
 
Thanks,
Jay