Nice explanation Kip,
If I may add a few more points.
If you look at the specs on the Panasonic 6.5AH "D" cell NIMH that the insight pack is based on, you will see that they are only specified for 500 charge discharge cycles. That would not get most of us through a year of use. The battery makers found that most of the life reduction with the cells comes when they are under the 20% SOC or over the 80% SOC. When restrained within that range, tens of thousands of cycles are possible. Presently only NIMH has the durability to last the 10-20 year life of the car.
The problem with the 20-80% SOC range is that the voltage stays pretty flat within that range, so SOC determination is difficult and must involve counting the amps used and amps returned, as well as adding temperature and rate of charge /discharge compensations. According to Honda the recalibrations that many people have are due to inaccuracies creeping into this formula, where the car looses track of where the batteries SOC is, so to be safe, when the software is unsure, they recharge to some point to recover. I still don’t totally buy that one, but until we have a better theory we are stuck with it. How do they know when to stop if they don’t know where the SOC is?
When fully charged, there is an easy to see rise then dip in voltage that happens at the 100% SOC point. If each recal is followed by a 100% charge, many of the people with frequent recals would have exceeded the 500 cycles.
Charge the batteries up without the car being turned on,(solar) and you take a real risk of overcharging the batteries, and shortening their life, as well as further confusing the SOC determining system.
As far as recharging on the fly with a solar panel, while it would work, the 150 -possibily 250W that one could fit on the upper surface of the tiny car would be a drop in the bucket. When My booster pack is turned on, I am feeding nearly 2800W into the battery, and I still have to be careful with assist or I will deplete the batteries. Of course I am applying aggressive assist at 100-125 MPG, to keep the MPG over 100, even climbing hills, so the electric is doing much of the work. After using my 2800W for some time, I feel that 4000-5000 watts from the booster system would be perfect. At that rate, I could nearly run off the boost, with the NIMH HV pack only acting as a buffer.
On the AGM batteries I was advised to not let the batteries get below 50% SOC and to always recharge immediately after use to 100%
All part of the care and feeding of batteries.