ORIGINAL: K-Bob
This may sound simplistic but I have to ask ..................... I have NOBS a A123s and my charge plug and my balance plug are both JR connectors. There isn't a chance that you are plugging the balance connector into the receiver? In addition 5.9 volts is pretty low for a A123, you should probably charge it anyway.
I have LiFe by EP Buddy and Hobbico. Both have Balancing Taps that either fit GP or TP chatge adapters. I have never seen Balancing Taps the look like JR servo leads.