I would also like to know this, as my battery was replaced a couple of months ago. The old battery would show 10.1 to 10.4 KWH at switch over. The new battery shows 9.6 to 9.9 KWH's, not much difference in distance has been noticed, maybe one or two miles.

 

Based on comments from WoponTour its based on what is used until CS mode starts. He gave the impession its an approximation, but not pre-programmed. Mine varies and appears to go down with high, long draws...climbing a long steep gade vs. gentle cruising. He cautioned not to apply across cars.

I also would like to know what is sensed and how it is calculated.

 

My guess is the switch to CS mode is based on state of charge...a voltage measure? a fast discharge will draw a battery down more quickly than a slow discharge....higher internal resistance/heating. You actually lose kwh at a high kw discharge. So you hit the trigger SOC at a lower time integrated kwh.

 

My guess is the switch to CS mode is based on state of charge...a voltage measure?

Agreed. Most battery packs are designed to cut off at a particular voltage.

That said, if I remember correctly, GM indicated that they designed the Volt to widen its usable SOC range later in the car's/battery's life to try to counteract the effects of battery degradation on EV range. So it does seem that kwh's-used can be factored in to determine when to transition to CS-mode, but probably only over the long-term.

 

It would almost have to be voltage, as has been suggested. As the SOC drops so does the voltage. The amount used will be affected by regen and also perhaps by temperature.