I'm using this to charge my N4 http://www.amazon.com/Motorola-SPN5689A-Universal-Charger-Titanium/dp/B007ZN5LE0/ref=sr_1_4?s=wireless&ie=UTF8&qid=1373326542&sr=1-4&keywords=motorola+usb+charger never had a problem. It only puts out 750mA takes about 2.5-3hrs to charge from 10 to 100%. And sometimes i use my old blackberry charger it takes longer since it only does 500mA. (I had these 2 laying around the house)

if you want faster charge time get something with higher amp output. The N4 will only pull what it needs so it doesn't matter what charger you get anyways.