Many auto's now have the battery in the trunk or under the rear seat (like mine does) and that handles the 100 cranking amps in sub zero temperature between battery and motor compartment.
Charging current would be insignificant compared to this!
Max.

 

if it's a low current trickle charge while driving that you want, consider something like this. But make sure to specify that you'll be plugging it into the cigarette outlet, lest it be considered an automotive modification.

This looks like it will be perfect. Thanks