In my Honda Insight, when I park for long time ( 2-3 weeks ) the NiMH battery pack self discharges. All battery packs do. So before I leave on a long trip, I run the car and charge the traction battery to the max. When I come back, the pack ( now 9 years old ) has lost significant charge. The "problem" is, the car doesn't know it. The dash SOC gauge still reads full, and because of this, when I get home and drive it and brake, I get little or no regen. At the same time, when I try to accelerate hard, there's no juice for electric assist. Still, the SOC reads "full". It takes about 30 minutes/miles for the Honda Insight to realize this mis-match, and the remedy is a battery "Recalibration" which immediately sends the SOC gauge in the car to zero, and the car does a slow, 10-20 minute recharge.

I don't see this in the FEH.

My FEH is now 4.5 years old. I sometimes park it for 2-3 weeks when I take my Insight on long trips. Like the Insight, the FEH NiMH traction battery will self discharge. Knowing this, I run the car before I leave and charge the pack to the maximum.... 53.0% in this case, before I park it.

I just returned from a 16 day trip in the Insight.
Before I even inserted the key into the FEH, I checked the low voltage battery. It was 11.7 volts. A bit low, but it's been 11.7 for a year now and is not getting worse. Then I inserted the key to "wake up" the car and my Scan Gauges. I know I parked with 53.0% SOC on the meter. Now, before even starting the car, the SG said the pack was 45.0% SOC.

So some how, the FEH can measure, and keep track of the SOC while parked, and the Honda either can't, or doesn't. I think this is amazing and cool.

*Some may think the FEH "predicts" the SOC based on some table of known discharge values. I don't think so... if that were true, the 45% would have only been an estimate, and the car would have readjusted once I drove a bit.
I watched closely for the following 15 minutes and 7 miles. The SOC went down and up normally, without any leaps & bounds to "recalibrate". Regen and assist strength were both normal.
-John

 

There's an A to D converter in there. The range Ford chose for the charge-recharge cycling has a very linear voltage to SOC characteristic. So if the voltage is X then SOC is Y.

The only issue as the battery ages is what amount of energy represents 100% as the real capacity decreases with age. Since the readouts are in % the net real energy avilable will decrease slowly over life, but I suspect that this will be barely noticeable until the battery really gets to end of life.

The only thing I can think of with the other guys setup is that the readout reads a stored number instead of the real time number. Until the system updates the stored number it reads out a false number. Only a guess.