Faulty Trakpower?

[himalaya]

Read each cell's individual voltage when charging, if the problem is due to a bad solder joint, you should read a high voltage(charger limits it to 4.2V by lowering the charging current) on one of the two cells, and the other remains normal. No possibility that the two output solder joints get weak at same time.

If both voltages read similar, I am afaid either you got a faulty pack or the Enerland cells inside gone bad with a significant rise in IR.