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Battery Degradation Test Results After 74K Miles.

7799 Views 23 Replies 14 Participants Last post by  bro1999
Here is the results of my battery degradation test. Data is collected from my Blink Charger. Problem is I never fully drain my battery, one of the only times this happened and I received a 100% charge was on May 23, 2012. Last June I decided to repeat that and arrived home with 1 mile remaining and turned on the heater until the engine started. I repeated that today.
My theory is that as the HV battery degrades, it will accept less of a charge. This data is going to try to quantify how much I have lost comparing these three data points at 9052, 53581, and 74400 EV miles. Gas miles was constant at 139 over this timeframe.
The result as the chart shows is there is no real change in the amount I can charge the Volt and I surmise that even at 3.5 years and just shy of 75,000 EV miles my battery is as good as new. Sorry, no new Volt battery pack for me



The SOC dropped to 18.8% when the engine finally kicked in:




Here is my SOC after I fully charged the Volt after this test:



I am really surprised, if that data is correct from Torque, this means 68.6% SOC window, not 65%. Maybe the buffer floated lower before the engine kicked in, I don't know. It did switch to gas, but the engine did not kick in for a little bit longer.
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Since, even in CS mode, the engine seldom runs below 25 mph and your test was at 0 mph, I suspect that it used a portion of the 'sub-zero' buffer before triggering your engine start.
 

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The car tries pretty hard to keep the engine off while stopped - I would expect it to go go thru most of the buffer before allowing the engine to start.
I've switched CS mode several times, while entering into my neighborhood, and was able to keep the ICE from starting with some smooth and easy driving (~0.3 miles).

EDIT: My motivation is due to not having to sit and wait for the ICE to reached operating temperature :)
 

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Discussion Starter · #5 ·
I did have the heat cranked on comfort though with temperature set to HOT.
 

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What is SOCu? Usable? In which case it appears you got an extra 5.5% of kWh on this charge, and that a "normal" 100% charge at your mileage would be 11.31kWh.

Which is quite encouraging! Whatever capacity loss may be happening seems to be "invisible" to the car so far.
 

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If the car is programmed to maintain available kw-hrs then the max % SOC will climb as total battery kw-hrs declines over the years. Has anyone seen that this is happening?

KNS
WOT has stated there is no on the fly SOC window widening.

I have a 2012 with 32k miles (26k EV), and I have observed no discernible degradation. In fact, if anything, my observed kWh used number after depleting the battery has gone UP a little (from 10.2-10.4 to 10.5-10.7).
 

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How is kWh for full charge measured, does that include any thermal condition the car might do to the battery or anything when it is charging, or is that the estimated that goes straight to the battery?

I think as the battery degrades, the amount of energy for a full charge will decrease as your capacity decreases, but I could be wrong. When I have a bad NiMH for my radio control car or something, it charges for 5 minutes and says it is done. It isn't accepting more charge, it accepts less and provides less.

I think Li-ion state of charge is measured by its voltage, so any degradation in the battery could be measured by seeing how much power it can provide with the same starting and stopping voltages. In other-words, the kWh used figure should decrease with aging (which you haven't seen, always reporting mid/upper 10s?) . I wonder if a more accurate power meter could be used? The built in meter does account for regen braking by subtracting it off, so this is good.

Weird, I notice the HV volts is the same before and after charging, the car must have some sort of voltage regulator to keep it the same? I would expect it to vary from 300 to 400 V. If this is true, we can't see how low the car is allowing the battery voltage to drop? In which case the lower voltage limit might decrease as the battery ages (expanding the usable range).
 

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The HV bus voltage has always seems to move in a remarkably narrow range to me. A Tesla battery has quite a bit more voltage swing. Granted they use a much bigger charge window too.
 

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I am really surprised, if that data is correct from Torque, this means 68.6% SOC window, not 65%. Maybe the buffer floated lower before the engine kicked in, I don't know. It did switch to gas, but the engine did not kick in for a little bit longer.
I guess that the Volt extends the SOC window over time to avoid Leaf effect.
 

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I guess that the Volt extends the SOC window over time to avoid Leaf effect.
WOT and others at GM have stated there is no on-the-fly SOC window widening.

The "Leaf Effect" is due to Nissan not wanting a liquid cooled battery TMS like the Volt.
 

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The kWh Used display is not a meter and it's not a measurement. It's an approximation estimate based on assumptions the car is making.
I don't see evidence to support this, I think it is a meter and directly measuring current in and out of the battery. Maybe I am wrong, but my guess is it is counting coulombs (integrating current) into and out of the battery using a hall effect sensor(s), this way it can easily account for energy added via regen braking, etc. This is a pretty standard way to meter Li-ion battery SOC, calibrated to Voltage at full charge and discharge. The current counting should be very consistent if the sensors are accurate, and I have noticed that the kWh used display in the center is fairly consisitent.

Temperature changes in the battery cause voltage changes which could change how much current you could draw from the battery before the battery is dead (voltage reaches a specific value). Temperature changes the available capacity.

My guess is variations between different cars could be due to cell balancing with some cars (has a weaker cell in it), I am sure some cell balancing is done, but maybe still enough to leave a 5% variation between cars (just an educated guess at percentage). A 5% variation could mean one car gets 9.5 kWh and another gets 10.5 kWh if 10 kWh were the target.
 

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To better illustrate your point, you should be using a full scale chart showing 0-12 or whatever scale.
I hate when people use zoomed in charts to mislead (not saying yours is, just that way too often it is used this way)
 

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WOT and others at GM have stated there is no on-the-fly SOC window widening.

The "Leaf Effect" is due to Nissan not wanting a liquid cooled battery TMS like the Volt.
The leaf effect happens also Norway and here in Finland, but not as drastic as on some hotter climates. With leaf you are degenerating from day one, but with Volt it's suspiciously level curve. If it smells fish and looks fish, it's most likely a half blind parrot.
 

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The leaf effect happens also Norway and here in Finland, but not as drastic as on some hotter climates. With leaf you are degenerating from day one, but with Volt it's suspiciously level curve. If it smells fish and looks fish, it's most likely a half blind parrot.
Well, I know for a fact that my car hasn't opened the window significantly yet, and we all know that Ari's car hasn't - because he just posted absolute state of charge information from Torque which matches the original new specification (and I have a meter rigged up in my DashDAQ that also uses the absolute SoC values.)

If the window had been opened, the car would be reporting more than 88% when fully charged, and less than 20% when it switches to gas (I know he has 18.8% in the photo - see the discussion above about his methodology and how it interacts with the Volt's programming wrt engine off when parked.)
 

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Unless the "window widening" adjustment is made at the nominal battery capacity layer of the battery management software layer such that it hides the widening from the values reported to Torque. What? You don't believe in conspiracy theories? :)

Seriously, a 3 year old car driven 70,000 miles on a recharged battery should be seeing at least a 5% loss of energy capacity. Five percent is still barely small enough that any apparent EV driving range loss could be obscured by changing levels of tire wear, climate conditions, or driving skill.
 

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If you look at GM and LG Chem's charts, the battery chemistry is well on track with negligible degradation after 3 years.
It goes to 15years and still only 85% of original capacity (15% loss)

Never charging to full really helps.

And yes, to the battery widening., we will never know.
The battery computer is doing its calculation and telling the main computer SOC is x%. It could very well be hidden in there.
However, I don't think GM would have any reason to lie (some might view this is a positive thing to advertise - maintain performance of day 1 for years to come) and a couple sources have said specifically that it does NOT increase the window.
 
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