INL provides interim data on FFE battery degradation

[michael]

Idaho National Laboratory has a fleet of four FFEs, and they have published the battery capacity when nearly new, and after some use.

The original data is available at

http://avt.inl.gov/fsev.shtml

Summarizing and approximating.....

Vehicle ID 1700 Miles 12K Original battery 24.2kWH Now 21.9 kWh Loss 9.5% in 14 months
Vehicle ID 2578 Miles 12K Original battery 24.8kWH Now 22.3 kWh Loss 10.1% in 14 months
Vehicle ID 4791 Miles 4K Original battery 24.4kWH Now 23.2 kWh Loss 5 % in 4 months
Vehicle ID 8207 Miles 4K Original battery 24.0kWH Now 23.3 kWh Loss 3% in 3 months


So roughly 10% loss of battery capacity in a year and 12K miles. At 22 months/39K miles my battery has about 17kWh useful, so it's down 15%. Either the rate of degradation slows, or the treatment I've been giving it is paying off.

If we assume original battery typically 24.5 kWh, 82% usable, then initially 20 kWh usable, goes down from there

 

[hybridbear]

That rate of loss seems rather high! Our Fusion Energi has lost no appreciable capacity in the 12,500 miles we've driven in the last year. It also sat for about 15 months before we bought it. I'm curious to see what happens with our FFE over the next year until we give it back.

 

[michael]

By comparison (same study)

2013 Leaf ID 7885, 16K miles and 13 months, dropped from 23.9 to 20.5 kWh (down 14%) so slightly, not dramatically worse.


I could spot only this Leaf and two FFEs that were tested when nearly new (< 1000 miles) and again around 12-16K miles.


It's possible your Energi has lost little if any capacity even if the above are typical. As a PHEV, it's battery may be less stressed than the FFE. On the other hand, it has a different TMS, I don't know what temp range it maintains. Studies puslished on the internet indicate Volt keeps it battery much cooler than does the FFE.

Also, early capacity fade is hard to spot. Until recently, I wasn't convinced I had seen it in mine.

 

[hybridbear]

It's possible your Energi has lost little if any capacity even if the above are typical. As a PHEV, it's battery may be less stressed than the FFE. On the other hand, it has a different TMS, I don't know what temp range it maintains. Studies puslished on the internet indicate Volt keeps it battery much cooler than does the FFE.

Also, early capacity fade is hard to spot. Until recently, I wasn't convinced I had seen it in mine.

I would think that the PHEV battery might be more stressed than the FFE since it goes pretty high on a full charge (98.8-99.5% of max SOC) and goes pretty low when empty & in hybrid mode (14% SOC). It also does not have liquid cooling, but the car does try to keep the HVB from getting much above 95 F in the summer (ambient temp higher than 70 F). It usually lets it get about 20 F warmer than ambient in moderate temps (50-70 F) and when it's colder than about 50 F the Energi wants to keep the battery around 55-65 F. One thing that the Energi does to protect the HVB is that if the absolute SOC is below about 20% the car will often start charging immediately when plugged in, overriding the Value Charge settings, so that the car is not sitting with a low SOC for hours before Value Charging begins. It will usually charge up to around 25% when it does this. The other thing is that while we have done 12,500 miles in 10 months (and the car sat for about 18 months after manufacture before we bought it) we have done lots of highway driving where we are not using the HVB. We usually use around 105 kWh per month in the Fusion & 210 kWh per month in the Focus Electric (according to each car's trip meter). That means we're doing more cycles in the Fusion since it has a 7.2 kWh battery and the Focus battery is about 3 times as large but is only used twice as much each month.

 

[michael]

It didn't occur to me that energi would use so much of its battery capacity. Volt is known for using a relatively small portion and for keeping the battery quite cool.

It turns out that INL has in fact tested Fusion and C-max Energi and their testing supports your observation: there is very little battery degradation, even at 40,000+ miles. They have tested Volts beyond 60,000 miles, also with just a few percent battery degradation. However, in both cases the results are ambiguous because they covered the majority of those miles using gasoline, not charge depletion...the battery was lightly used. It would be interesting to see how a Volt performs if used as most people do so...around 75% on electricity, gasoline only when unavoidable.

 

[michael]

Further review of the INL report shows that they did a baseline test of vehicle 8207 and found approximately 19.5 kWh usable (varied slightly with test conditions). Comparing this with their initial test of that same vehicle's battery (24.0 kWh) it appears that the usable percentage in their test was 81%, very closely in line with the 82% we have been estimating here.