How large is negative impact on battery life from MAX RANGE charging?

jimratliff said:

It seems like all of Tesla's public discussions of range (e.g., 300 miles for the 85kWh battery) are based on the assumption that you'll charge the battery at Max Range rather than Standard. However, the display will tell you:



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Can anyone help evaluate how large is the negative impact on battery life? Is this just a legalistic disclosure of a small effect? Or is this a big deal?

If the negative effect were a huge deal, it would seem a little misleading to advertise a battery range that you can only achieve by degrading your battery.

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I'd guess that there isn't definitive data to answer your question yet. There have been recent stories discussing how the testing done on individual cells might overstate the amount of degradation in a well managed pack like exists in the Model S.

But there absolutely are small negative effects from doing a max range charge. Any single such charge has a negligible impact, but even small effects add up over time. The worst case apparently comes from letting the vehicle sit for an extended period of time at a max range charge without using it. So its recommended that when you do a range charge, you schedule it so that it finishes charging right before you leave. I think you would need to be particularly abusive to notice a measurably larger degradation over time than most users would experience.

I don't think there is any false advertising involved. The car will continue to operate, you will just experience somewhat faster degradation. There are many things that an ICE vehicle is technically capable of doing, but which will result in additional wear and tear if you do them.

For example, a conventional ICE vehicle will experience far more degradation on the transmission (a very expensive component) if you are routinely changing your speed and acceleration than will occur if you maintain a constant speed on level terrain for the life of the vehicle. The Model S doesn't have this problem. Are ICE manufacturers misleading you by not pointing this out to prospective customers? At least the Model S gives you a warning, while I don't recall any ICE vehicle coming with a sticker warning customers to avoid excessive gear shifting.

Anyways, here is a recent story about battery degradation -

Design News - News - Can EV Batteries Last 20 Years?

An important note; they say that fast charging can damage the battery. That is certainly true in many cases, but Tesla is adamant that their SuperChargers can be used as often as you want without damaging the battery. I've heard the cooling fans on the Model S kick in when SuperCharging, so my assumption is that they are aggressive about keeping the batteries in the proper temperature range, despite the fast charging.

Many on this thread have said that the amount of time spent at max charge is the key variable. I hope someone can help me understand why this is. My current understanding is that battery degradation is due to swelling of the anode that leads to cracking, and that the swelling is due to the state of charge. In this simplest explanation, the state of charge is causing the damage and not the time spent in this state.

Thanks in advance for the clarification.

Martini said:

Many on this thread have said that the amount of time spent at max charge is the key variable. I hope someone can help me understand why this is. My current understanding is that battery degradation is due to swelling of the anode that leads to cracking, and that the swelling is due to the state of charge. In this simplest explanation, the state of charge is causing the damage and not the time spent in this state.

Thanks in advance for the clarification.

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My DS explained it like farmers doing crop rotation and leaving some fields fallow. Normal charge leaves 10% of capacity unused, and the sophisticated battery management system rotates which cells are unused when. A max charge uses all the cells leaving nothing spare. So in his explanation if you max charge right before or during a road trip when you will immediately drain that 10% and more, any impact should be minimal. However you don't want to max charge and leave it sit in that full state. Makes sense to me logically, but I'm not an engineer.

One data point regarding my Roadster, which I drove for 3 years, approximately 60,000km. I used range charge about 3-5 times per year, and did not let the car sit at maximum range for more than an hour after charging. My degradation in range was less than 5% over the 3 year period which seemed to be completely normal.

dj905

Martini said:

Many on this thread have said that the amount of time spent at max charge is the key variable. I hope someone can help me understand why this is. My current understanding is that battery degradation is due to swelling of the anode that leads to cracking, and that the swelling is due to the state of charge. In this simplest explanation, the state of charge is causing the damage and not the time spent in this state.

Thanks in advance for the clarification.

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From what I can gather from this article, there are multiple mechanisms that degrade NCA lithium ion batteries: http://www.nrel.gov/docs/fy12osti/53817.pdf

Here are some relevant quotes from the article:

"From the system perspective, significant stressors to a lithium-ion (Li-ion) battery include exposure to high temperatures, exposure to high states of charge (SOCs) and charge voltages, calendar age, depth of discharge (DOD), and the rate and frequency of charge/discharge cycles."

"Mechanisms for capacity loss include fracture, isolation, and chemical degradation of electrode material, as well as permanent loss of cyclable lithium from the system as a byproduct of side reactions."

"Under storage conditions, the dominant fade mechanism is typically growth of a resistive film layer at the electrode surface. As the layer grows, cyclable lithium is also consumed from the system, reducing available capacity."

Doug_G said:

That's not how the battery works. All the cells work all the time.

This is a chemistry issue with the cells themselves. They degrade slowly over time, and being fully charged slightly increases the rate. Same thing if nearly empty.

The simple answer: don't hesitate to use Range mode when you need it. A few hours are insignificant. Just don't leave it in Range mode for months at a time.

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Doug, I heard the same thing from my service manager: that the cell subgroups (about 70 cells/ea) are rotated to reduce the number of charge cycles per cell, thereby extending the life of the pack. Is he wrong?

ToddRLockwood said:

Doug, I heard the same thing from my service manager: that the cell subgroups (about 70 cells/ea) are rotated to reduce the number of charge cycles per cell, thereby extending the life of the pack. Is he wrong?

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I also read a similar statement that the subgroups of cells would rotate use to ensure longer life.

Doug_G said:

The simple answer: don't hesitate to use Range mode when you need it. A few hours are insignificant. Just don't leave it in Range mode for months at a time.

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Perfect advice. Good post