BUMPPPPP!!!!
Drove 30 minutes with iPhone XS Max in the under arm rest USB port playing music and maps and it maybe charged 10%.. This has gotta be the lowest amp charger.
Honestly though I’d assume that both USBs come from the head unit radio. It’s not directly coming from the vehicles power. Going through anything; computer, clock, radio; will always be slower charging than direct. So I really don’t think there’s anything we can do besides radio swap to aftermarket maybe. Doubt it’s a fuse swap or something quick and simple. Also the radio head unit itself gets REALLY hot. So not sure I’d want to mod the radio potentially causing bigger issues.
I guess if you need a real quick charge then plug in to the vehicle and Bluetooth to radio.