I'm facing the same problem using my HTC with gps in my car.
i ran some test at home with a app called fast discharge to drain battery and monitor the battery using battery monitor. Battery drain is about -850ma on battery
Test are made during one minute with log of current every 10 seconds.
1)ORIGINAL wall HTC charger+ORIGINAL cable, detected as AC, battery is still charging about 300-350ma (with still fast discharge draining battery at -850ma)
1)ORIGINAL wall HTC charger+3RD PARTY cable, detected as AC too, BUT battery is discharging about at -50 ma (with still fast discharge draining battery at -850ma)
What is the conclusion? Even a AC detected cable but not original won't charge the battery as well as the original one. But why? Is there a chip in the cable? Are 3rd party cable to thin?
Thank you for your help.