I have a drawer full of micro usb chargers. I figured that any of these would charge the thunderbolt. I was wrong. The charger that came with the thunderbolt is 1000 ma. Some of my junk drawer chargers vari from 300 to 800. Those make the little lightning bolt show up and the notification light turn orange, but the battery doesn't gain power. Only the 1000 (aka 1.0 amp) chargers and plugging the cord into my laptop charge the phone.