USB Charging Newer devices

[vaderag]

Short version: what is the best way to charge a newer device from a USB port that only outputs 0.5a?

Long version:
Been out today in my new car and tried charging my phone from the built in usb... didn't do anything. Makes the charging noise on the phone but no charge.

Obviously I'm guessing it must be only outputting at 0.5a which is very low for today's devices... what can I do? Is there any way to bump up a 0.5a to higher easily (appreciate this might vary by a billion factors, but guess the USB is coming off the car's 12v rails somewhere along the line...)

Another thought that came to me was putting a battery pack that charges slower in the middle, but i don't know if this will work given that i'll probably be drawing more than i'll be getting in to it... and can they even charge as they are outputting?

Any thoughts welcome!!
Cheers

Xperia Z5 on Marshmallow

 

[vaderag]

Unfortunately the only one is in quite an awkward position for the gearstick... Ideally I'd like to find a way to use the USB that's out the way, but that is my fallback....

 

[vaderag]

I can't seem to find the spec, but given that I have a cheap car adaptor that is rated it 0.5 and I have a 1 charger here which gives enough to charge, im pretty certain it's 0.5