I bought a car charger from RIM for my Curve 8330. Most of the time, it does charge the Berry (plug icon appears). Sometimes though, I'll plug the Berry into it. The Berry lights up, meaning it recognizes that it's been plugged in, but the plug icon doesn't show up, meaning it's not charging. The green LED is always on when the charger is plugged into the car's socket, so that means it's working.
What could possibly cause it to fail to charge the Berry sometimes?