You say that your charger is an Extrema.
What little I've read about that charger indicates that it has no A123 mode.
Are you charging as if they were LiPo's? Or does your version have an A123 specific set up?
I have been using A123s for well over two years (Over one year as motive power) but have always used an A123 specific charger.
The FMA 4S first and for the last year the FMA 10S.
Each has a specific mode for these cells.

Or, have you found your problem in the meantime.