CARS II ,
It is critical that we know the brand battery you are using.
Since A123 cells (known as Linp or LiFe M1) are So vastly different from other LiFe cells, the use, care, and management of your batteries will be different.

The nano plate technology is roughly 100 times more robust in true A123 cells. Therefore my comments assume you are using A123 cells since you indicated they are 2300mah size.

Keep in mind that voltage drop in a healthy A123 cell begins around 2000mah. Establishing a safe minimum discharge level, say 50% capacity is very important. NO ESV out there is sufficient for use to determine if an A123 has enough capacity to continue to fly. You must know remaining capacity percentage, not voltage, since cells drop voltage quickly below a radio's needs under load.

Since an A123 cell spread from empty to full is only .3 volts, an imbalance of more than .1 should be considered a NOGO. Let's assume you always charge using an A123 balance charger. An imbalance larger than .05 may indicate the pack was discharged too much. Either it was left connected too long or too many flights on a charge, or the balance tap continuity reached the receiver due to an install problem. Always disconnect batteries from the radio switch harness between flying sessions.

In your case since cell number one is at a higher level than cell 2, it may be that cell 1 was the cell that discharged too much. If the load such as a receiver, was seeing the balance tap it will draw cell 1 down as if it were a 1s battery. Weaker cells charge up faster. The cc/cv software sees that voltage in cell one hit max sooner and drops to a very slow charge rate that can be as low as around 100mah. This can go for a long time as the charger tries to balance the pack and get cell 2 caught up without damaging the pack.

There are little devices that can allow you to charge the cells individually and manually re balance them. But I would first find out what discharged the pack too low. Most often it is waiting too long before recharging or not balance charging every time. 4 years is not too long for an A123 battery. So age alone is not reason to retire a pack. However if you can't get that pack balanced to within .05 or so then I would not use it in an airplane. Keep it as a bench pack.