Problem: Full charge capacity dropping

[dickhillpdx]

I have been leasing a 2018 Chevy Bolt EV since February 2018. At first, it got 238 miles (or more) on a full charge. Since September 2018, the full charge capacity has gone down, from 210 to 190 to 170 to 150 and, most recently (December 30, 2018), 130 miles. NOTE: This is the full charge capacity and does not take into account weather, use of accessories, etc. In addition, the weather now (December) is about the same (or warmer than it was) last February when I first got the car. The car has 5750 miles on it.

As it went down, I talked to the Chevy dealership. They said that the car had re-programmed itself in light of my driving habits. (I drive mostly in the city of Portland, Oregon, but every few months, I drive to Tacoma, Washington, about 150 miles). With the full charge capacity of 130 miles, I can no longer drive to Tacoma without stopping, even if I drive no faster than 55 MPH and use no heat, radio, etc.

I have a few questions of the forum:

1. Has anybody else had this problem?
2. If so, what did you do?
3. Is there a way to fix the problem (and get back (or nearly back to) the full charge capacity I had last February?

 

[WetEV]

I have been leasing a 2018 Chevy Bolt EV since February 2018. At first, it got 238 miles (or more) on a full charge. Since September 2018, the full charge capacity has gone down, from 210 to 190 to 170 to 150 and, most recently (December 30, 2018), 130 miles. NOTE: This is the full charge capacity and does not take into account weather, use of accessories, etc. In addition, the weather now (December) is about the same (or warmer than it was) last February when I first got the car. The car has 5750 miles on it.

As it went down, I talked to the Chevy dealership. They said that the car had re-programmed itself in light of my driving habits. (I drive mostly in the city of Portland, Oregon, but every few months, I drive to Tacoma, Washington, about 150 miles). With the full charge capacity of 130 miles, I can no longer drive to Tacoma without stopping, even if I drive no faster than 55 MPH and use no heat, radio, etc.

I have a few questions of the forum:

1. Has anybody else had this problem?
2. If so, what did you do?
3. Is there a way to fix the problem (and get back (or nearly back to) the full charge capacity I had last February?

There have been other electric cars with capacity loss like this.

There are several possible issues. Getting the dealer to troubleshoot this correctly might be the biggest issue.

What you can do to diagnose the problem:

Run the car as close to empty as is reasonable. Plug into a charging station that records the energy delivered. Some public charge stations do this, as you are billed by the kWh. Other public charging stations will report it as well. Take the number of kWh the car takes for the charge, and multiply it by 0.9 and you have about how much energy the battery received. Multiply by the inverse of fraction of the battery that was charged. If you discharged to 10%, then the total capacity of the battery would be Delivered_kWh*0.9/0.9, which is about delivered_kWh.


With a fairly accurate estimate of the battery capacity, now go talk to the dealer again. The range estimate or GOM (Guess-O-Meter) isn't good evidence, as it depends very much on how you drive. A recharge test is good evidence. Sure, the charging loss isn't exactly 10%, probably a few percent more or less. The battery isn't at 25C, probably colder, so the capacity would be a few percent higher if measured at 25C. But you are likely not more than 10% off, if done carefully. While the If the loss is enough to trigger the capacity loss warranty, or less than about 36 kWh, then the dealer should do a warranty replacement or repair. Based on you not able to drive 150 miles, I suspect that this is the case.

Drive Motor Battery Coverage
Propulsion Battery Warranty
Policy (Bolt EV)
Like all batteries, the amount of energy that the high voltage “propulsion” battery can store will decrease with time and miles driven. Depending on use, the battery may degrade as little as 10% to as much as 40% of capacity over the warranty period. If there are questions pertaining to battery capacity, a dealer service technician could determine if the vehicle is within parameters.

if the capacity isn't below 36 kWh, it sounds like it will be there soon. The dealer could do still do a "cell balance voltage" test, especially at a charge level below 20%, and might spot a very weak cell.

I suspect you have a single very weak cell. The dealer should replace that cell, or the whole pack. Other possible issues include a Battery Management System (BMS) fault.

 

[SeanNelson]

I have been leasing a 2018 Chevy Bolt EV since February 2018. At first, it got 238 miles (or more) on a full charge. Since September 2018, the full charge capacity has gone down, from 210 to 190 to 170 to 150 and, most recently (December 30, 2018), 130 miles.

The car's range estimate does NOT tell you the battery capacity. It is an ESTIMATE of how far you'll be able to drive, and it's based on many factors which influence the number you see. These include your recent driving habits, the air temperature, whether or not you're using heating or A/C, etc. etc. etc.

To get an idea of your battery capacity, charge the car to 100% so that the energy usage numbers on the Infotainment screen reset to zero - then drive it to as close to empty as you can. Before you plug in to recharge again have a look at the kWh consumed - that'll tell you how much energy came out of the battery to get you that distance.

 

[keijidosha]

I have a few questions of the forum:

1. Has anybody else had this problem?

http://www.mychevybolt.com/forum/viewtopic.php?f=12&t=8079

"We ran another test on our battery capacity a few days later. This test indicated each 5% is now worth 2.19 Kwh which calculates out to a total battery capacity of 43.9 Kwh. The battery continues to diminish in capacity and is now at 27% loss of capacity."

 

[citonyc]

it does state that the battery range capacity will be affected by temp and altitude, but that's a insane decrease. try keeping a log for about a week then bring it back to the dealer with your trend log. possibly a defective cell or other component in the battery system.
I just picked up the 2019 Bolt a week ago, but ill keep a eye on that also

 

[Mwagers]

Did you resolve this? Mine just dropped from 60kWh to 44kWh. The dealer said it was because I'm driving with too much weight and in hot weather (he wants to get rid of me). My advice to any potential Bolt buyers: but a Tesla. Chevy only cares about you up to the point you pay them.

 

[WetEV]

Did you resolve this? Mine just dropped from 60kWh to 44kWh. The dealer said it was because I'm driving with too much weight and in hot weather (he wants to get rid of me). My advice to any potential Bolt buyers: but a Tesla. Chevy only cares about you up to the point you pay them.

Don't confuse Chevy and GM with the dealers. Several people have posted similar problems, and resolutions. For example:

http://www.mychevybolt.com/forum/viewtopic.php?f=12&t=8079&start=10

 

[Mwagers]

I asked the dealer to check the cell voltages for a bad cell and they told me there isn't a problem unless the ECU has a code. They also claimed that the car would have a code if there was a bad cell, which is not the case for other owners with this problem. I was surprised to find that they have no equipment to discharge a battery. I guess I will be calling Chevy to see what they say. This is way too much work to get a 2 year old car fixed. Chevy has created a good system for making owners give up and go home with defective cars.

 

[mrdrmorgan]

Have any of you Bolt owners, who are having "battery capacity degradation" concerns, used TorquePro to measure the HV battery capacity and cell voltages for ALL cells? If you haven't, find someone who is using TorquePro and have him measure your battery capacity and cell voltages. The TorquePro data is much more accurate than trying to use the data from the Energy Information screen. You will be able to get what the car's current battery capacity is and the current State of Charge (SoC). I have been using TorquePro with an OBDLink MX OBD2 adapter for almost a year to measure the battery capacity and SoC on my 2 Spark EVs and the results have been great and believable.

 

[NeilBlanchard]

The range estimate is not the way to measure battery capacity.

Your driving, the temperature, elevation changes, weather conditions, road surface, tire inflation, how much you use the heater or A/C - all affect the driving range.

 

[Mwagers]

I contacted Chevy and I have an "advocate" who is supposed to help me get this resolved. I will wait to see how Chevy handles this, but I am not satisfied so far; the car could have been diagnosed by now and the battery order placed if not for the failure of Chevy's dealer service model.

Strange comment from @neilblanchard about using the guess-o-meter, since almost everyone here has gone beyond that. I'm wondering if you are a dealer, since this has been their de-facto response to my problem; your failure to provide a way to better estimate the battery capacity is also similar to the dealer response.

@SeanNelson's method of charging to full and driving to empty is a good first pass method to get a rough estimate of capacity (though I'm not clear how the infotainment system accounts for regen, but that should only be a small amount of energy). I am using the amount of energy added to the battery from the charge station over a known range of state of charge (SoC) i.e if I plug the car in at 10%SoC and charge to 100%SoC only 27 kWh goes in; it should take ~54kWh (0.9 * 60kWh).

I understand how EV efficiency works. I keep my tires at 50psi, and on my most recent trip I was driving on level roads (200ft maximum elevation change according to abetterrouteplanner), with the AC off, 70F outside temp with two passengers (250 lb total) at 55 mph; just about the ideal driving conditions. My efficiency was 5.5 mi/kWh. Up until now, at 5.5 mi/kWh, I have gotten--as the car should--280 miles out of 85% of 60 kWh battery (60*5.5*.85), I got closer to 140 miles before I stopped to charge at 15%SoC.

I have also been using TorquePro and I see that cell 29 is 3.85V with all of the other cells at 4.1-4.2V (I did not note the SoC for this reading). My version of TorquePro does not have "HV Capacity", but the "!Battery Level Guess" from Torque is near 60kWh, so I'm not sure what's going on there. I also notice that the "SoC Raw" diverges from the "Battery % DIC" as my capacity approaches zero (at 100% they are almost the same, but near 0% DiC the SoC Raw is near 50%. I'm almost certain Chevy has a bad algorithm that is failing to throw a code for this failure. I hope none of you have this problem because it is impossible to deal with Chevy. Also, when I fast charge, the rate drops from 55kW to 35kW at about 25% (it should drop at 55%) and drops again from 35 kW to 25kW at about 50% (it should drop at 70% or75%?), so it seems to be using SoC Raw to determine the charge rate cutoffs. The OP had the same problem with no code. Does anyone have any ideas what is going on based on the symptoms in Torque? Any help is appreciated!

 

[SeanNelson]

@SeanNelson's method of charging to full and driving to empty is a good first pass method to get a rough estimate of capacity (though I'm not clear how the infotainment system accounts for regen, but that should only be a small amount of energy).

If you go down a long hill you'll see that the "Energy Used" kWh value on the Energy Detail screen drops as regen adds energy back into the battery. So it appears to account for regen in the way that you'd expect.

I am using the amount of energy added to the battery from the charge station over a known range of state of charge (SoC) i.e if I plug the car in at 10%SoC and charge to 100%SoC only 27 kWh goes in; it should take ~54kWh (0.9 * 60kWh).

You have to be a bit careful of the energy shown by the charger because charging is not 100% efficient and the car's own systems can consume of of the energy as well. For example if the car is turned on with the heater running while charging then up to 6kW of the power from the charger will be going into the heater instead of the battery. And if the car needs to control battery temperature it can run the heater or A/C even if it's turned off.

Another thing to watch out for is Hilltop Reserve mode - if you're charging from an L1 or L2 charger then the car will complete the charge cycle at a state of charge well under 100%. And I haven't seen any DC Fast Chargers that do this, but it wouldn't surprise me if there were some out there that cut off at 80%, which seems to be a pretty widely agreed "recommended stopping" point for DC fast charging.

That being said, 27kWh seems awfully low if it really added 90% of charge to the battery.