Review on Optimized Motorcycle USB Charger with ON/Off Switch, Voltmeter, and SAE to USB Adapter (5V 4.8A) by Stephen Burgstaller

I used this to add a USB charging socket under the dashboard of my Honda S2000. The factory 12-volt socket is located between the seat backs. Adding a car charger is visually obtrusive, and so is running a USB cable from it to a device mounted on the dash or windshield. Running the cable under the dash is a much cleaner solution and this adapter worked great. Charging speeds are very reasonable, and the ability to turn off USB and upgrade at some point in the future is a huge plus.