hello, I have a 7100G.
I hve the genuine BB wall socket charger for my bb 7100g. My wife also have a 7100G (both have the same issue per below)

I can charge the phone from the bb wall socket charger and from the same cable using my USB port on the PC.

I have purchased off ebay, a 12v car charger for the bb7100g (non genuine) but it will not charge the phone. The lightning bolt next to the battery indicator comes up for a few seconds and then goes away.

I have read a few things around here that suggest that the phone looks for something on the charger (perhaps a grounded wire or something) that then enables the phone to charge.

I also have a USB MP3 player car charger that I charge my USB mp3 player. I get the same results from using that socket and the genuine bb USB cable. So there has to be something to do with the charger.

Any ideas?

my only option is to get a USB cable that is tested and works on the wall socket.. Cut it and see what is on each of the wires. Then use the same cable on my 12v charger and see what happens...