I have had some battery degradation and it was caused by overheating the HVB. The loss was determined after a hot summer in 2015 when the HVB reached max temperatures on several occasions. Once this lesson was learned I instituted an active monitoring of the HVB temperature using a ScanGauge. The HVB gets hot from both charging and rapid use from acceleration and regen. The gentler the HVB is used the battery for the battery.
A major consideration is the outside temperature. The hotter it gets outside the less external charging that can be done without overheating the HVB. I have also noticed that letting the car sit overnight will not necessarily be enough time for the HVB to cool down. Where I live if overnight lows are 80ºf(26.7ºC) charging of the HVB should not be performed at all.
The car will automatically limit use of the HVB at 113ºf(45ºC) but this was not enough to prevent HVB capacity loss. My goal in activity monitoring the HVB temp is to keep the temp below 105ºf(40.5ºC) and when possible aim for 102ºf(39ºC).
Here is the general rule I follow at the outside temperatures listed.
At 50ºf(10ºC) charging as often as desired.
At 70ºf(21ºC) Charging more than once a day should only be done with HVB temperature monitoring.
At 80ºf(26.7ºC) Charge only once per day.
At 90ºf(32ºC) Stop charging the HVB Or limit charging if actively monitoring the HVB.
During times of high temperature I normally run the car in Hybrid mode only.
Since I had the HVB degradation in 2015 and started following these practices there as been no additional lost HVB capacity.