I had a similar problem. When I first got the radio, I tried charging via the wallwart for over 12 hours. It wouldn't charge the stock pack over 7.0 v. I called Hitec and they were suppose to send me a new wallwart...but I haven't seen it.

I pulled the battery and charged it using my Triton. I had a charge cord with a Dean's mini plug. This time using .4 amps, it charged to about 8.5v. The problem was after about a day, the transmitter low voltage would start beeping.

I finally slow charged the battery using .1 amp for about 20 hours. That did the trick. Now my battery holds it charge for over a week and it's still 7.6 v.

It sounds like your battery charger is working. Maybe you should try charging it for 24 hours or hang on and someone will have a better solution.

Good luck!.