Odd Voltage behavior

Battery voltage (and hence the SOC%) takes a bit to stabilize after charge/discharge events. Driving in EV mode will do both and the battery quickly bounces between modes as acceleration and regen events occur. When driving, the battery is in a closed circuit state. After stopping, the battery is disconnected (open circuit) and takes a bit to "regroup" and voltage readings are very likely to be different than in an open circuit condition (how much depends on many factors including temperature and internal resistance of the battery cells).
I also suspect the SOC reading you are seeing is buffered a bit and also based somewhat on recent history - a bit like the range estimate. Dropping by a few percentage points after shutdown is likely within normal behavior.

 

This is a good point, and we have to remember that we're not measuring the charge by the same way that we would measure it for a lead-acid battery (specific gravity of the electrolyte) but instead by the output voltage. This is a good approximation of SOC for this type of battery, but it is going to take a short time to stabilize after charge/discharge cycles.

 

I bought a level-2 charger just so that I could do meaningful preconditioning. Probably the most expensive warm air on the planet when I divide the cost of the L2 charger by the number of times I'll precondition.

The only engineers who can untangle all the mysteries work for Honda. But I enjoy the challenge of reverse-engineering the systems, while recognizing that the conclusions we reach may be totally bogus because they are based on limited information.

 

Ray B

The 12 V SoC fluctuates similarity to what you describe for both the Clarity I drive and another a friend drives. In round number...12.3 - 13.9 are the measured norms with outliers in each direction of course.

Hope this helps.