Battery degradation - Chevrolet Volt Forums: Chevy Volt Forum
 
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post #1 of 4 (permalink) Old 04-14-2020, 11:41 PM Thread Starter
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Battery degradation

We own a 2012 Volt with 83600 miles and the vehicle is near the end of the 8 year/100,000 mile battery warranty. Historical observation of information on the onboard screen in the car establishes that 12 + kwh would be routinely discharged before the generator took over and the battery power ended. I also monitored charging from the 220 volt charger in our garage, and 13 kwhs plus being used to charge the car to full were not uncommon. Unfortunately, Blink no longer provides charge information, so its been a couple of years since I've tracked how much power went into charging. However, 13 Kwh going in, given the inefficiency of charging batteries, is consistent with 12 plus kwh being available for discharge, and being discharged.

Lately I noticed that the most that can be discharged is 9 kwh, at which point, the generator takes over. I took the car to the dealer today concerned that being able to only discharge 9 kwh meant that over 25% of the range of the battery is no longer useable. Dealer found no error codes, and GM technician contacted by the dealer by phone referenced Document ID 5406682 to assert that the minimum battery warranty capacity was 33.6 Amp/hrs, and that, based on the in shop technicians testing, all cells tested at 3.98 volts, and the battery capacity was at 37.8 Amp/hrs. Basically, GM's position is that the battery is within spec, and the is no warranty claim.

Have others encountered loss of battery capacity issues with their Volts? (Capacity has a direct effect on range - you might not notice how many kwh are capable of being used, and instead see a drop in range). And, as it now appears, GM takes the position degradation of the battery within a range it established is acceptable for purposes of the warranty, yet at the time the purchase of the car was being considered, nothing was disclosed about the 8 year/100,000 mile warranty meaning that, if at or near the end of the warranty period/mileage, experiencing at 25% plus loss of range/battery capacity was acceptable.
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post #2 of 4 (permalink) Old 04-17-2020, 01:19 AM
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"all cells tested at 3.98 volts, and the battery capacity was at 37.8 Amp/hrs"

It is normal.

8yr/100K miles is battery defect warranty. It only kicks in when battery or power train fails. That is the standard industry EV spec and warranty.

GM battery warranty is about 30% degradation during this period (only among few EV company that actually offers capacity warranty). It looks like your Volt is well within that degradation and doing fairly well. No battery last forever and it would be against the law of physics if it doesn't degrade over time with use.

2011/2012 Volt has usable battery capacity between 9.6kWh to 10.3kWh.
2013/2014 Volt has usable battery capacity around 11.4kWh
2015 got another bump to about 12.1 kWh.

Assuming that your Volt 83K mile is mostly electric, then the battery has experienced over 2,000 cycles (at the rated 35 miles per charge). At that point, the battery should degrade naturally about 5-10% in capacity at least if it is well protected and managed.

Cycle count and aging are the two biggest factor in natural degradation. Thermal protection is also important but it is directly related to aging. Hot temperature accelerates it.

I have a 2012 Volt with over 100K miles and it only used about 463 gallons of gas so far. But I can see about ~10% degradation in EV range. As battery ages, the first sign of degradation is that generator will come on earlier at low energy state due to the fact that battery won't be able to keep up with the current demand at those low power state. This is normal for all battery degradation.

Of course, the larger the battery is, the higher the mileage for a given cycle. For example, Bolt EV is rated for 259 miles of EV range and it has about 66kWh battery. So, for a similar 2,000 cycles, the Bolt EV would have clocked over 500K miles.

There is a 2012 Volt in OH called Sparky that made to about 380K miles before it had a problem.
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post #3 of 4 (permalink) Old 04-17-2020, 02:13 PM Thread Starter
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Thanks for the info gtls1. After posting I did more digging and have concluded that the degradation experienced on my Volt is within the warranty specs, although on the high side - i.e. closer to that 30% number than other. Perhaps that is due to often recharging to full even after shorter trips, instead of routinely waiting until battery has been more deeply discharged. Otherwise our Volt is basically a garage queen, used as a commuter car almost exclusively for local driving only (other high mpg ICE vehicles available for long distance driving).

Curious, and on a slightly different note, I've upgraded an older sailboat (12v DC system) and installed 690 watts of solar and lithium ion phosphate batteries (400 amp/hr for the house bank; 120 amp/hrs for crank, using a separate dedicated AGM for bow thruster - both the AGM battery and the crank battery have 45 watt panels to keep them at or near a full SOC). Those LIPO batteries are expected to be able to go through some 30,000 to 40,000 charge cycles (assuming no significant discharges below 10%, while with AGM's, if well managed and with few discharges below 50%, and proper controls to minimize off gassing issues when recharging the last few % of capacity, you might get 4000 cycles if you're lucky). There is no battery conditioning going on with the boat's batteries, and, with solar, the batteries are constantly being charged/topped off when sun is available. How important is conditioning re extending battery life/resisting degradation? And, is the practice of constantly charging negatively impacting battery life? And, as to the 4000 cycles for the Volt's batteries, isn't that count on the low side given the type of batteries?
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post #4 of 4 (permalink) Old 05-15-2020, 01:48 AM
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Like I said, it is almost impossible to measure the % degraded with some special diagnostic tools. The display is never precise enough due to a wide range of factors. The usable battery is about 10.3kWh. You would have to lose 3kWh before it gets closer to 30%. That would mean that your car would switch to gas at 7.2kWh after a full charge.

Lithium iron phosphate is completely different chemistry. It generally last 2x or 3x the cycles as those NMC (Volt and Bolt battery) or NCA (Tesla) chemistry. The cycle counts are generally for full charge/discharge cycles. If you only use a portion of it, then the cycle count goes way up. If a battery is rated for 4,000 cycles with 5-95% cycling, then at 30-70%, it can potentially reach 8,000 cycles or 10,000 cycles. The best way to keep lithium ion battery healthy in general is to keep it under 60 deg C. Never ever exceed that. the cooler the better. In general, Lithium ion battery likes the exact same temperature rate as a human being. It loves 60-75 deg F. Now, some chemistry generates more heat than other. Lithium ion phosphate generates little to no heat. NCA generates far more heat when discharged or charged at great than 2 C (C is the term describing the rate. For example, 1kWh battery charging or discharging at 1kW is said to be 1 C. Discharging/charging at 2kW is considered to be 2C. A 16kWh battery discharging at 100kW would be 6.25C)

Battery also degrades over time naturally even if you don't use it. Some chemistry are worse than others. The higher the energy density, more likely it will age quicker and generate more heat but they generally have far higher energy density so that is the trade off.

If you don't use the battery for a long time, then it is best to store it at 40-60% charge. Don't ever freeze it which will shorten its life. Low temperature storage around 10deg C or 50 deg F is ideal at 40% charge.

The battery on the Volt is designed to handle over 6,000 cycles. But Volt battery is never fully charged even if you do fully charge it. It only cycles between 10% to 90%, owner can never breach that range so it would last longer. it is also temperature monitored (heated and cooled) to keep around 77 deg F all the time.

None of those cycles mean that they don't degrade slightly in those cycle count. It means that they usually don't lose more than 30% of its capacity in those cycle counts.
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