The Rayovac PS70 Dual USB Car Charger is a nice little gadget that I’m using in my car to charge my smartphone. It can be had for just a few bucks, e.g. $8 at WalMart. Although its output current is specified at 2A (or 2.1A in newer versions), it charges many devices at a low current of only 0.5A because it doesn’t correctly identify itself as a fast charger. This can be easily fixed.
A lot of devices (e.g. Samsung Galaxy S II, LG Nexus 4, LG Nexus 5) do not switch into fast charging mode (called AC mode in Android), because they do not detect the Rayovac as a charger; instead, they stay in data transfer mode (USB mode) and charge at 0.5A. That’s not only very slow, but also not enough for charging or even just compensating battery drain when using the phone for music and navigation while driving.
Fortunately, there’s an easy fix if you haven’t got two left hands. All you need is a soldering iron, solder and a flat screwdriver or something similar.