I have a SOC reset device that I bought from M. Dabrowski. It is a plug and play OBD-II device. Here is the link :
http://99mpg.com/projectcars/socresetdevice/
With this device I can set the SOC gauge to 19 or 6 bars on 20, Set the IMA battery module fan to fast or slow speed and reset both MIL and IMA lights. When I take my car after charging it I set it at 19/20 bars and I usually am at 2 or 3 bars when I arrive from my commute.
I charge at only 338 mA with the fan always on so I don't think there is much battery deterioration. I try to maintain it active and use my car at lest 1 day per weak so it is not self discharging too much. So far my 8 years old battery seems in pretty good shape since I started to grid charge it. It gives full assist for a good amount of time and can take a lot of regen before being "full charge".
When I do my Charge and discharge process every seasons exept winter (brrr..) I check the Amp/hour of the battery and I get 6.5 or 6.6 every time. When my battery will begin to be really finished I will buy a bumblebee battery
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About the cruising speed I cannot tell a constant speed. I do P&G cycles of 52-39-52 mph on the highway. The max is 62 and the min is 37.
My city driving is mostly flat some up and downs from viaducs but nothing big.