From personal experience, the charger must output between 600 to 800mhA, anything higher or lower and it stops charging. This is from my casual observation of using a low output charger and once trying to use an Apple wall-to-USB plus with a 2000mhA rating.

The best solution was to get a Blackberry charger which I use that outputs at 700mhA. I read that this was fixed in a power-kernel, but not sure where exactly I read that.