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Discussion Starter #1
Has anyone found a good way to determine usable battery capacity without doing a full discharge? I know the leaf has a battery life graph.

I think I am now around 50kw total capacity. This is based on usage vs % of battery. Seems a bit early to be down that much as I am only at 34k miles and just over 1.5 years in service. Charged almost exclusively to 85% (nightly) and normally only discharged to about 50%. Never run out, but have been down in the bottom 1-2 bars 3-4 times.
 

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With a Volt, even a full discharge isn't. The Volt maintains a buffer to make sure the batteries are never drained completely, thereby prolonging their longevity.

You may be doing yourself a disservice. There are posts about people who do lot's of top off's rather than full discharge/recharge. Lots of small top-offs can negatively affect the kWh Used algorithms.

See https://gm-volt.com/forum/showthread.php?62593-kWh-Used-vs-Battery-Degradation-FAQ
and https://gm-volt.com/2013/02/26/a-tale-of-two-volts-the-summary/
 

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I can verify capacity is a lot less than 60kwh now, just not sure how much less. This is a Bolt, not Volt. Last Wednesday I did a 280 mile trip in 10 deg weather and was down to 1 bar left upon returning home. With htr active I was able to input 46kwh charging. Thus from almost empty to 85% charge is in the low 40kwh assuming a 10% ish charge loss. That suggests I have 50 or less kWh available from full charge to empty.

I am lazy and don’t want to run it in the garage with full heat until dead then recharge. I was hoping that there was some method or obd output that can provide battery capacity other than full discharge and charge. If I am really down 16% in 1.5years, which seems high, do I change charging habits for better life or abuse it more to make it fail?
 

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This is a good question from Bolt users. With the Volt, it is simple, you just drive to exhaustion and complete trip on gas, then when you shut down the display shows you amount used (the one time I did that it was 10. something so I'm good). With a Volt you have not gas back up so if it has similar display results you would have to do something like what Slotracer said. I wouldn't rely on any algorithm to calculate any accurate measurement as battery use measurement isn't linear and so is just an approximation. Is there any other way?
 

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I can verify capacity is a lot less than 60kwh now, just not sure how much less. This is a Bolt, not Volt. Last Wednesday I did a 280 mile trip in 10 deg weather and was down to 1 bar left upon returning home. With htr active I was able to input 46kwh charging. Thus from almost empty to 85% charge is in the low 40kwh assuming a 10% ish charge loss. That suggests I have 50 or less kWh available from full charge to empty.

I am lazy and don’t want to run it in the garage with full heat until dead then recharge. I was hoping that there was some method or obd output that can provide battery capacity other than full discharge and charge. If I am really down 16% in 1.5years, which seems high, do I change charging habits for better life or abuse it more to make it fail?
Did you have Hilltop Reserve turned on? That will prevent the Bolt from being fully charged.
 

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Did you have Hilltop Reserve turned on? That will prevent the Bolt from being fully charged.
Yes, it was on, but it stops at 85% or two bars down from full. That should be about 6kwh as there are 20 bars per charge. I started 1 bar from empty and stopped 2 bars from full, adding 43-44kwh. Even if each bar is a full 3 kWh my capacity is now 52-53kwh. If the capacity is truly lower, then each bar is also less, somewhere in the 2.6-2.7 per bar.

Based on my range today of a full charge being 148 miles after doing the same drive in 50 deg weather. I think my battery has degraded, just trying to determine how much without going to the trouble of doing a full discharge.

For reference the difference in range is huge between 10 deg and 50 deg f. Coming home at 10 deg, I barely made it 60 miles to my mid point charger starting with a 3/4 charge. Averaged just over 2m/kWh. At 50 deg, I used about half a charge and was about 3.5m/kWh.
 

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Yes, it was on, but it stops at 85% or two bars down from full. That should be about 6kwh as there are 20 bars per charge. I started 1 bar from empty and stopped 2 bars from full, adding 43-44kwh. Even if each bar is a full 3 kWh my capacity is now 52-53kwh. If the capacity is truly lower, then each bar is also less, somewhere in the 2.6-2.7 per bar.

Based on my range today of a full charge being 148 miles after doing the same drive in 50 deg weather. I think my battery has degraded, just trying to determine how much without going to the trouble of doing a full discharge.

For reference the difference in range is huge between 10 deg and 50 deg f. Coming home at 10 deg, I barely made it 60 miles to my mid point charger starting with a 3/4 charge. Averaged just over 2m/kWh. At 50 deg, I used about half a charge and was about 3.5m/kWh.
I think charging can be affected by temperature. Even though the battery is heated the total capacity when charged may be affected by the colder temperature. The only way to be sure would be to see how the battery performed within a more moderate temperature range such as 70 - 80F.
 

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Has anyone found a good way to determine usable battery capacity without doing a full discharge? I know the leaf has a battery life graph.

I think I am now around 50kw total capacity. This is based on usage vs % of battery. Seems a bit early to be down that much as I am only at 34k miles and just over 1.5 years in service. Charged almost exclusively to 85% (nightly) and normally only discharged to about 50%. Never run out, but have been down in the bottom 1-2 bars 3-4 times.
Seems to me that if you take a long drive, then divide the kWh Used for the drive by the change in battery raw state of charge for the drive (using an OBD reader, perhaps?), you would have the kWh contained in each 1% of soc. Multiplying that by 100 would give you the full battery capacity. That won’t give you the usable window, but it will give you a general idea about whether or not the amount of power contained in the "usable window" has diminished because the full capacity of the battery has diminished.

Example:
Full charge = 85% raw SOC
End of trip = 15% raw SOC
kWh Used for the trip = 56.9 kWh
56.9 kWh / (85-15)% SOC = 0.813 kWh/1% SOC
100% SOC battery full capacity = ~81.3 kWh

An example from the numbers you posted in comment #4, where you normally charge to 85%, and used 46 kWh as you drove from an 85% SOC to an "almost empty" SOC (perhaps 15%?), then:

46 kWh / (85-15%) = 0.657, full battery cap = 65.7 kWh.

Think of the results of this method as an approximation of the current full battery capacity. The precision of the measurements you record is limited (displays show what... a single decimal place?), so you’re dividing a rounded off number by a rounded off number. Also, the accuracy of the calculation improves as the size of the change in SOC approaches 100% of full capacity, so a short drive produces a rougher guess than a longer drive. If for you, "full" is 85% and end of trip is only ~50%, that’s not a large sample.

For Volt owners trying this, keep in mind that once the car "switches to gas," the generator kicks in and normal operations will see a raw SOC reading fluctuate around the "switch to gas" number (i.e., kWh Used won’t change while driving in Extended Range Mode, but take the reading at the moment of switch to gas because it might be different later).

Perhaps it would also be wise to obtain multiple sets of data (i.e., several trips) to see if the calculations produce relatively consistent results.
 

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I did the following:

Fully charge
Take a trip of about 230 miles, no A/C or heat (ventilation only). I limited speed to under 70 mph. Temperatures were moderate (60's, 70's)
At this point I had used a little over 60 kWh and was in "propulsion limited" mode

I then stopped in front of my charging station, opened all the windows and ran the heater full blast. This was drawing 5-6 kW

Car shut down after about half an hour with "Out of Energy, Charge Vehicle Now!" message at 63.2 kWh
 
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