Many Insight battery packs develop an imbalance.
Sitting at a constant SOC for a long time without charging or exercise will allow the individual cells to self discharge due to internal leakage. This leakage is usually slightly different on each cell, so given enough inactivity time, the pack will develop a big difference in charge between the cells.
The Insight system stops charging at 80 % SOC, so the imbalance never gets fixed by an equalization charge.

If you fully charge a pack with a constant current of 85 -255 MA, this constant current will bring up the weaker cells by giving all cells a 100% charge.The cells are rated for 500 or more full cycles, so an occasional one or two will not effect the pack life.
It is very likely that many packs that have become imbalanced, and were frequently recalibrating before throwing an IMA code can be revived by rebalancing.

a solar pack charger that provides the required current at sufficient voltage to do this recharging and re-balancing is described here.

The solar charger needs to be able to produce 180VDC to fully charge the battery.The panel output terminals with no load will be at 250VDC. this panel delivers about 15 watts of power.
Using this procedure exposes you to the full pack voltage, so you can get electrocuted if you get your self across the HV, of either the pack, or the solar panels.
I will be testing this system on some local people that have recalibrating battery packs. An AC powered charger/balancer is on the list of projects, but will not be as safe, or as green as this purely passive PV method.