Is it fair to say GM will eat a lot of money on battery warranty work?

If the GM BAS Hybrids were any guide, Yes!

FIRST RECALL

Models: 2007-2008 Saturn AURA Green Line Hybrid
2007 Saturn VUE Green Line Hybrid

Condition
General Motors has decided to conduct a Voluntary Emission Recall involving all 2007 model year Saturn AURA Green Line Hybrid and VUE Green Line Hybrid vehicles and certain 2008 Saturn AURA Green Line Hybrid vehicles. A battery case condition on these vehicles may cause a voltage imbalance in the hybrid battery. If the imbalance exceeds 0.6 volts, the check engine light will illuminate and hybrid function will be disabled. If this occurs, the charge/assist gauge would show no movement, the fuel economy light (ECO) would not illuminate, and the vehicle will be powered by the gasoline engine only.

Correction
Retailers are to replace the 3 hybrid cassettes that make up the battery assembly.



SECOND RECALL

MODELS: 2008-2010 Chevrolet Malibu
2007-2009 Saturn AURA, VUE
Hybrid Vehicles

CONDITION
General Motors has decided to conduct a Voluntary Emission Recall involving certain 2008-2010 model year Chevrolet Malibu and 2007-2009 model year Saturn AURA and VUE hybrid vehicles. The hybrid function on these vehicles may become inoperative. If this occurs, a "Check Engine Light' will illuminate in the instrument panel and/or a "Service Hybrid" message will illuminate in the Driver Information Center, the engine will run in the gasoline engine mode, and fuel economy would be reduced.

CORRECTION
Dealers/retailers are to replace the hybrid batteries and reprogram the engine control module.

 

It's really hard to test real-world conditions. Automotive service is extremely harsh. Given the GM propensity to under-engineer, I wouldn't be surprised if they have even more battery problems than Honda.

 

Volt is using only 10.6 kWh out of the entire 16 kWh pack. That should also increase the number of cycles because those are just partial cycles that caused the least wear.

Having said that, GM warranty documentation expects Volt battery to have 70% of the original capacity after 100k miles. That means it'll be doing 100% depth of discharge (full cycle) to provide the same 35 EV miles. The battery will come to a quick death.

We have no idea how GM tested beyond 150k miles. It is possible they put more miles on the gas engine.

 

The biggest strain on the batteries would be charging the top 10% or draining the bottom 10%.
Since the Volt doesn't give you access to that, it should help heir batteries last long than if users could deep cycle the batteries.
That being said, this is new tech for GM and I don't have a lot of faith in their engineering and QC, which is why I lease
As for the amount of money they will be putting out for warranty work, that doesn't really matter to me.

 

Well 1750 full cycles at 1 cycle a day breaks out to about 4.8 years by itself, so 3 years seems pretty pessimistic.

Also keep in mind, with a longer range battery fewer charges are full cycle. You can run 15 to 20 miles and still only need a half charge. I'm no electrical engineer but my understanding is less deep charge discharge cycles have less effect on battery life (like the bazillion of mini cycles in typical hybrid operation of a prius).

 

GM is not worried about the cost of warranty work. When they go bankrupt again they'll just get another bailout. I don't think it much matters which party is in power.

 

If you can keep the discharge floor around 20% to 30% and the upper charge limit to 80% to 85%, you can get multiple thousands (2000-5000+) of discharge cycles on new lithium iron phosphate cells. Make it 90% range, and you are down to less than 1000. With Lithium-Ion, Lithium-Polymer, Lithium-Cobalt and Lithium-Manganese you wont even come close.

The volt uses LiMn2O4 (Lithium Manganese Oxide) which is inferior to LiFePO4 (Lithium Iron Phosphate) in every way including cycle life. However, it is cheaper which is the trend with big3 companies.

10/16 of the pack is usable, or 62% of the pack. This suggests they are staying in the 20% to 80% type range, which gives the best cycle life to depth of discharge figures for any lithium chemistry. I would speculate based on 60% depletion, 50C temps, and ~10C charging there would be 1200 or so cycles to dead. Stay in the 80% to 70% range and you can probably double that life expectancy. So if you drive the volt 35miles a day or something so that you go from full to empty and the CS mode kicks in, you probably won't get many years out of the current battery. Admittedly, this probably effects a small percent of the drivers.

I would be surprised if they don't realize soon that they need to swap their packs for LiFePO4 instead of LiMn2O4 where the additional cost upfront will be paid back in less warranty work and less irate customers 5 years from now. Either that or make the capacity/range ratio bigger. Larger pack same range, or same pack and smaller range.

 

I don't think anyone can say this for certain unless they are a firmware engineer at GM.

However, I believe (unsure) that the CARB warranty states that failure is when a certain percentage of initial pack capacity is deemed gone. Not that the range is decreased or anything like that. So if you have a 16KWh pack, then you must be able to put in X% * 16KWh in 10 years or else it is a failure. Which would mean this "trick" wouldn't work for warranty evasion.

The above needs to be verified.

 

The numbers pulled from the CAN bus show 20-87%. Absolute minimum SOC is 15% (the point where it goes into Reduced Propulsion).

The ICE comes on at 20%, ramps charge up to 22% as it warms up, and maintains approximately 22%.

 

I am not aware of anything published that supports your conclusion. Do you have a reference that states the car will expand usage to maintain EV range?

I'm pleased that GM, unlike Nissan, commits to a limit. I guess that's why there's not a similar thread in the Nissan forum, right?

 

The info is about a year old but I was able to find it. I guess you were not following the Volt a year ago.

Now GM finally admits the Volt will actually use 65% of the total energy storage capacity of the battery. That amounts to 10.4 kwh.

The engine generator will turn on once the battery hits somewhere between 20% and 25% state of charge, which equates to 25 to 50 miles of EV driving. When fully recharged, the battery will acutally be kept at a maximum 85% to 90% state of charge.

As the battery ages and energy storage capacity of the lithium-ion cells degrades, control units will widen the percent state of charge band to continue to deliver the range goal.

By 8 years/100,000 mile when the battery warranty ends, GM expects the car’s range to be reduced by 10 to 30 percent in the worst case. Some customers will experience less degradation. The car can continue to drive beyond that point, but range will continue to contract.​

Source

 

Then it seems they are maintaining the "happy range" for lithium. However the use of LiMn2O4 instead of LiFePO4 is a pretty big determination of cycle life. Not to mention cells with Manganese in them have the potential for thermal runaway (hence the active cooling). Some LiFePO4 cells have no Mn additives and can basically be exploded by an overcharge with the net result being burning acidic goo but no fire or smoke. Do that with a cell that has Mn in it, and you get a lithium fire that almost nothing can put out.

Well I guess I can stop protecting GM. It seems to come from them and that would be horrible. Expanding the SOC range by a few percent gives an exponential dropoff in cycles. So they are pushing the SOC limits so that the range is good just past warranty and then it will drop dead.

 

I don't think there is official word from GM but this makes sense to do on battery operated devices, and there are whispers. If your figure is right the battery is charged to 13.9 kwh, as the max lowers from 16 it makes sense that the "full" charge level would not decrease as much. The battery is degrading but I do not think that at the age that this is likely to happen charging a higher percent but lower level won't significantly accelerate degradation. I doubt they will change the 20% level as this would cause faster degradation. Only time will tell. I doubt we will know for a large number of years how these batteries age.

This is a good thing, but I think those regulations make them commit. Nissan does allow the user to charge to 100% to degrade the batteries faster, or 80%. This makes it harder to warrant.

 

Yea, that's why I think they'll need to reduce the EV range or prepare to replace the battery under warranty.

The third choice is to gradually fade the EV range so it may make 10 years but 150k miles is 50% more than 100k. I doubt they'll be able to stretch that far without a redesigned battery.

 

The key warranty number on these batteries is years not miles. Toyota outside of carb also warrants 8years 100K miles, but then claim 400K miles on some prii. I don't think we will know that 8 year or 10 year number until more years are done, but they attempt to age the batteries in tests, the charge discharge is easy. I'm also sure they are looking at battery improvements all the time.

 

Just to point out the obvious..... Toyota will face the same challenges with the PiP and battery studies indicate that the smaller pack size used in the PiP will be under more inherent life cycle stress than a larger pack because of increased opportunity charging and higher regen/discharge ratios to battery size. I don't think Toyota or GM are eager to have many cars needing battery replacements under the 10 year or 150,000 mile warranties starting with next year's CARB-state Volts and PiPs.

I'm sure both of their battery suppliers were tweaking the design to meet the warranty up until the last moment. It's been reported that LG Chem mixed in some Nickel and Cobalt to their otherwise Manganese Spinel cathode and may also have tweaked their electrolyte additives based on technology they licensed from ANL.