Charging in a car

It will charge but super slow and certainly not when it's switched on.

 

Tried this. If you USE your MacBook while it's charging, it will actually not sustain its battery strength, it will drain, albeit more slowly. If you leave it alone, it will charge but take SEVERAL hours to complete the charge. This is the only charger on Amazon that produces the proper output (29W is 14.5V at 2A) to charge at the same speed as the original adapter, but it ships from China in a month from now.

Helper Mini 14.5V 2A 29W Car Charger Car Adapter USB-C for New MacBook Mac Book Retina 12" with 5V 2A USB https://www.amazon.com/dp/B01E47PWEI/ref=cm_sw_r_cp_tai_i7SuxbH59BVB0

Anything charging over a USB-A connection won't produce or shouldn't allow the power that a straight USB-C cable does, as it's not designed for that. Any manufacturer that tells you so is wrong. And any generic USB-C charger still won't produce the wattage for the MacBook, as they're designed to charge newer USB-C smartphones.

Of course, a quicker solution is to get a cheaper inverter so you can simply use your original adapter as if it's plugging into an AC outlet.

 

You'd be cheaper buying a small inverter and installing it in the car.

 

This would be a better option:

http://www.amazon.com/BESTEK-Power-...&qid=1465442324&ref_=sr_1_1&s=pc&sr=1-1-spons

 

I second or thrid the inverter thing. My SUV has 110v AC built in but the inverter is the best way to go.