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Discussion Starter · #1 ·
Just picked up a late model year 13 LT. Battery has good amp hours(44.9/48) and range, and cells were even during first test drive.
First full charge however showed cell #2 at .04v higher than the rest, and .02v lower at depletion.
I’m charging back up and took this screenshot about 1/2 way.
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The good news is that the seller will take it back if there is anything substantially wrong with it. We have a week or so to decide.
I’ll take a reading tomorrow with ~20% charge and under load. What other signs or diagnostics should I look at, and what’s everyone’s feeling on this?
 

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If it were me, I'd take a reading from the fully discharged state using Service Mode to avoid intermittent reading changes due to power draw. I'd look at the overall voltage in this state as well as any (substantial) differences in the cell groups. The .02v difference at depletion you referenced wouldn't cause any concern.
 
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You can't measure the cells while they're charging as they're being actively balanced and the values are changing as you are reading over the cells. You read at full depletion and full charge, ideally with the car unplugged.
 

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Do a search for "121mv", and you will find all the info you need to make a good educated guess on the state of your battery.
 

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Overall, the battery initially looks good. A few more look-sees at full and empty will fill in the story. Spreads are good. Keep an eye on #2.
 

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Discussion Starter · #7 · (Edited)
So here is a shot with battery depleted under load, with #2 dropping to 3.505v:
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Charged some then tested under load again. Diff. of .38mV:
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I’ve read Jaryd’s descriptions of 121mV being the tipping point, and that 3.45v is the minimum acceptable voltage for any cell.
Should I walk away from this Volt, or are these numbers not as alarming as they seem to me?
 

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Why do you believe a cell group low voltage of 3.45v bricks it?
According to the (Gen2) Service Manual, a DTC is set for a low cell group voltage condition of .02v. The discharged minimum voltage reading on my 2017 is 3.432v, with a .072 delta and no errors. As WopOnTour has stated, it's not that simple, which is why I did some reading through the Service Manual myself prior to my warranty going.

I'd spend $20 for a subscription for the Gen1 Service Manual and verify the cell group DTC triggers for that model year. Either that, or just move on to a different car so you don't have to stress out over the battery.
 

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Discussion Starter · #9 ·
Why do you believe a cell group low voltage of 3.45v brick it?
You’re right - that wasn’t accurate on my part. He said that 3.45 - 4.05v is the acceptable range.
That’s exactly why I’m looking for as much input from others as possible. I’m fine with cells being off spec a little if it’s not a sign that things are heading south. Just getting as much information as possible so that I can either walk away or feel confident in the purchase.
 

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You’re right - that wasn’t accurate on my part. He said that 3.45 - 4.05v is the acceptable range.
That’s exactly why I’m looking for as much input from others as possible. I’m fine with cells being off spec a little if it’s not a sign that things are heading south. Just getting as much information as possible so that I can either walk away or feel confident in the purchase.
The cell voltage ranges listed and the voltage spread are looked at in conjunction with a DTC. My voltages have been outside of the range listed in the SM for mine, however a DTC hasn't been triggered, as it's still well within the Hi/Low voltage DTC trigger values. IMO the battery voltages you've listed are healthy. However, there's no guarantee that the battery won't go bad, or that monitoring the cell group voltages will reveal a problem in time.

Given the financial impact of a battery going bad, I've started to take a few minutes every 5-10k miles to collect the data. I'll be looking for significant changes in voltages over time as well as the cell balance. I believe the likely best metric to view for the battery health would be the cell internal resistance. The system does have a DTC threshold for resistance, however that data isn't available via the MyGreenVolt app.
 
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If you have not had any PPR (propulsion power reduced) event messages that’s a good sign.

I have not had any for a few weeks.
 

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Given the financial impact of a battery going bad, I've started to take a few minutes every 5-10k miles to collect the data. I'll be looking for significant changes in voltages over time as well as the cell balance. I believe the likely best metric to view for the battery health would be the cell internal resistance. The system does have a DTC threshold for resistance, however that data isn't available via the MyGreenVolt app.
Perhaps the question is how to identify if you have a "battery going bad" or if you merely have a "battery losing capacity over time" (as all batteries do)?

You could trigger a PPR event in a brand new Gen 1 Volt by driving too aggressively with a fully depleted battery (e.g., by driving fast up steep mountain roads) until the reserve in the buffer couldn’t keep up with the demand. As the battery loses capacity over time, it takes a lesser and lesser amount of high-power-demand aggressive driving with a fully depleted battery to trigger the PPR event. Often the first symptom of loss of the original full capacity is that after you stop the car, the PPR event occurs when you restart it.

How can one distinguish between PPR events such as these that are the product of aggressive driving combined with a normal loss of battery capacity over time, and any PPR events that may be triggered by "weak cells" or a "battery going bad?"

The 2011 Volts are now 10 years old, and the battery warranty, in a sense, was reassurance that the battery would not normally lose more than 30% of its original full capacity before the car turned 8 years old... my 2012 Volt’s battery, now at 9 years old, seems to have lost no more than 13% of the original capacity (and I just drove 42.7 ev miles using 9.5 kWh in the full charge today!), but then, I’m still well under the 100K miles portion of the warranty spec. At what vehicle age should it not be unusual to find your Gen 1 Volt "full charge range" is now only 20-25 ev miles in good weather because the battery has lost capacity but is otherwise still healthy?
 

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<snip>
At what vehicle age should it not be unusual to find your Gen 1 Volt "full charge range" is now only 20-25 ev miles in good weather because the battery has lost capacity but is otherwise still healthy?
Looking at my data and gazing into my crystal ball, i will guess at around 15 - 16 years after manufacture,
 

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Perhaps the question is how to identify if you have a "battery going bad" or if you merely have a "battery losing capacity over time" (as all batteries do)?
When the changes in the battery are not relatively consistent over the cell groups, but you have 1 group going rogue. If the changes are even, then it normal wear & range degradation. I do have less range (same route/speed/conditions) then when new, so I'm sure I have some normal degradation. Monitoring the voltages may be of no use in the end, but it only takes a few minutes of time every 3-6 months, so the cost is low. The best indication would be the internal resistance. Our Volts do monitor this. There is a good article on that aspect here:
Guide: Battery internal resistance – what, why and how?
 
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Discussion Starter · #15 ·
When the changes in the battery are not relatively consistent over the cell groups, but you have 1 group going rogue. If the changes are even, then it normal wear & range degradation. I do have less range (same route/speed/conditions) then when new, so I'm sure I have some normal degradation. Monitoring the voltages may be of no use in the end, but it only takes a few minutes of time every 3-6 months, so the cost is low. The best indication would be the internal resistance. Our Volts do monitor this. There is a good article on that aspect here:
Guide: Battery internal resistance – what, why and how?
I have a 2012 that only has 32.9 amp hours (of 48Ah original), so 31.5% degraded. Cells are perfectly even in all conditions. The 2013 only has about 7% degradation in Ah. Is there a way to read internal resistance using GDS2? I know that weak cells are supposed to lower the overall resistance and thus functioning of the battery, but am not sure how to measure these effects or rate of degradation other than looking at individual cell behavior.
 

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Is there a way to read internal resistance using GDS2?
There's no way that I know of to see that information. If someone else knows I'd be interested as well.
 

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Chevy Volt 2013, 250k km still 13,8kWh battery for 70-75km. driving 53km to work daily
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I tried check it via current (OHM law U/I=R) In fact try connect the mygreenvolt, found a nice hill, and ride constantly slow, lets say about a 20km/h. check if the difference between cells is OK. Now, push the accelerator pedal near the full position, and let the car accelerated constantly. Let the mygreenvolt read the battery voltage twice or more, not changing the pedal position. Try remember the difference, and if any, which cell have significantly lower voltage. Slow down and return home :)
From this measurement you can indirectly decide if the pack is in good condition or not, no matter what is the capacity degradation.
As smaller is difference between cells on high load, as better your pack is.

Its my way to try the battery condition.
 

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I tried check it via current (OHM law U/I=R) In fact try connect the mygreenvolt, found a nice hill, and ride constantly slow, lets say about a 20km/h. check if the difference between cells is OK.

Its my way to try the battery condition.
Hello
155k miles!
Have you had many or any PPR events?

what delta volts is used as max. Still the 120mv?
 

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Chevy Volt 2013, 250k km still 13,8kWh battery for 70-75km. driving 53km to work daily
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No PPR yet, only "no charging issue", repaired by reprogram units.
I can still drive 70-75km per charge, cca 9,5kWh usable. Difference is cca 8mV on fully charge, 16mV near empty. On load is imbalance around 50mV.
This is from my today drive:
1626309198324.png
 

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Discussion Starter · #20 ·
Update: dealer Volt tech said cell balancing had already been done. Went ahead and updated the BECM.
He suggested that if the cells remained unbalanced wit the update we should back out of the sale.
 
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