Is Charging to 100% Really that Bad?

[sdorn]

It seems fairly accepted on the forums that charging to 100% and letting the car sit for more than an hour should be avoided as it can cause faster degradation over the long term to the battery.

The number of times I've seen this basically universal advice on TMC over the past few weeks lead me to wonder if there is any evidence of how bad this actually is for the battery? Are there people that have regularly charged to 100% and let the car sit for 8 or 12 hours repeatedly over several months (or years) and experienced increased degradation as a result?

One of the reasons I ask is because my Nissan Leaf (which is being upgraded to a P100D as soon as my car is delivered in December) has no ability to charge to anything other than 100% unless you unplug it manually. As a result, I charge it to 100% every single day, and it sits there at 100% for at least 8 hours most nights and sometimes for several days. I've had the Leaf for about 1.5 years now and haven't seen any sort of reduction in range or anything like that.

Is the Tesla battery technology more susceptible to this type of degradation? Is this really only a concern for those that plan to own their car for 5+ years?

I'm not asking because I want to regularly charge my car to 100%. I will follow the recommended charging guidelines Tesla suggests when my Model S comes, but I was very curious as to how people arrived at the 1 hour figure and whether there was any evidence showing how damaging sitting at 100% is for the car.

 

[wdolson]

I have never even been in a Leaf, but I have heard they have more battery degradation than Teslas have had. I know Nissan had to replace the batteries in some early Leafs under warranty because of severe degradation. It's possible Nissan has some circuitry in there that makes charging to 100% impossible and the reported capacity is only the usable capacity. The current 60 KWh battery from Tesla is essentially like this.

This article goes into the technical details of what happens charging Li-ion batteries to 100% as well as a number of other charging scenarios
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

I normally charge to 90% and have only charged to 100% once, though I charged to 95% a couple of times on a recent road trip. For most driving situations, you don't really need more than 90% on a day to day basis. It's rare my car is ever below 200 miles of range remaining.

 

[Saghost]

Leafs in hot environments have seen degradation of fifteen percent in a year due to the combination of always charging to 100% and not having any battery cooling system.

If you go to the my Nissan leaf forums, you'll find a bunch of big threads about this, the lawsuit they owners filed, and the warranty improvement and battery replacement policy Nissan was forced to offer.

The heat is a significant factor, though - if the battery stays cool it won't degrade as fast. Tesla has one of the best thermal management systems in the market, so their batteries stay cool.

I don't think we have a good example of what an abused Tesla battery will degrade like, but there are some national lab studies on impact of sitting at SoC and temperature floating around somewhere for generic lithium batteries.

 

[DJ 240V]

Since 60 has a software limited battery capacity that is actually 75. Does this means that even if I charge the car to a 100% , I'm only actually charging to 80% of the battery capacity and thus it's safe to do so?

 

[Saghost]

Since 60 has a software limited battery capacity that is actually 75. Does this means that even if I charge the car to a 100% , I'm only actually charging to 80% of the battery capacity and thus it's safe to do so?

Assuming they limit the battery by preventing charging to the top as the Supercharging rates suggest, you're correct.

That's what they did with the 40s, and the evidence suggests that they've done it again, but I don't think we're completely confident of that yet.

There are a bunch of threads on that topic...

 

[jbcarioca]

There is lots of discussion and explanation about this in this sub-forum. The net is that because of the Tesla BMS Tesla battereis are far less sensitive to high SOC than are others. Still, as the article linked by wdolson and many other articles do point out the inherent SOC issues with li-ion batteries:

I...
This article goes into the technical details of what happens charging Li-ion batteries to 100% as well as a number of other charging scenarios
How to Prolong Lithium-based Batteries - Battery University

...

because of those issues Tesla recommends staying between 20% and 90% SOC for daily use. That is normally pretty easy to do. For trips going to 100% or going below 20% reportedly has no material effect on battery longevity. Checking the user reports shows that quite a few tesla drivers charge to 100% every day and make long drivers. Most seem to charge to 100% just before driving but some just let the car sit.

All of that makes me think we are probably better off following the normal recommendations on a day to day basis but the odd departure either above or below seems to do no harm. There is the LA taxi service that charges to 100% every day and had lost only 6% capacity after 100,000 miles. That seems pretty good to me.

 

[sandpiper]

Since 60 has a software limited battery capacity that is actually 75. Does this means that even if I charge the car to a 100% , I'm only actually charging to 80% of the battery capacity and thus it's safe to do so?

Actually no. You'd think that that would be the case, but (as I understand it) Tesla actually simulates battery degradation. They determine the anticipated range of an actual 60kwh battery based on mileage/ charging behavior / driving behavior and so-on. You can anticipate the same general level of degradation from 100% charging as you would with a regular 60kwh battery.

They do this to encourage people to upgrade to the 75. A 60 that you could 100% charge all of the time and that doesn't degrade becomes pretty close to what a 75 is.

 

[sandpiper]

Just kidding! 100% charging the 60 should be fine.

 

[msnow]

It seems fairly accepted on the forums that charging to 100% and letting the car sit for more than an hour should be avoided as it can cause faster degradation over the long term to the battery.

The number of times I've seen this basically universal advice on TMC over the past few weeks lead me to wonder if there is any evidence of how bad this actually is for the battery? Are there people that have regularly charged to 100% and let the car sit for 8 or 12 hours repeatedly over several months (or years) and experienced increased degradation as a result?

One of the reasons I ask is because my Nissan Leaf (which is being upgraded to a P100D as soon as my car is delivered in December) has no ability to charge to anything other than 100% unless you unplug it manually. As a result, I charge it to 100% every single day, and it sits there at 100% for at least 8 hours most nights and sometimes for several days. I've had the Leaf for about 1.5 years now and haven't seen any sort of reduction in range or anything like that.

Is the Tesla battery technology more susceptible to this type of degradation? Is this really only a concern for those that plan to own their car for 5+ years?

I'm not asking because I want to regularly charge my car to 100%. I will follow the recommended charging guidelines Tesla suggests when my Model S comes, but I was very curious as to how people arrived at the 1 hour figure and whether there was any evidence showing how damaging sitting at 100% is for the car.

I've read on this forum from people that charge to 100% often (in one case everyday) and from others who have technical knowledge of Lithium ion batteries that say keep it to a minimum and don't let it sit. If you charge to 100% and leave your charge setting at 100% a warning pops up on the 17" screen advising that successive 100% is not recommended from Tesla. Since it's under warranty for 8 years and Tesla keeps log data from each car why chance it?

 

[Electric700]

Leafs in hot environments have seen degradation of fifteen percent in a year due to the combination of always charging to 100% and not having any battery cooling system.

If you go to the my Nissan leaf forums, you'll find a bunch of big threads about this, the lawsuit they owners filed, and the warranty improvement and battery replacement policy Nissan was forced to offer.

The heat is a significant factor, though - if the battery stays cool it won't degrade as fast. Tesla has one of the best thermal management systems in the market, so their batteries stay cool.

I don't think we have a good example of what an abused Tesla battery will degrade like, but there are some national lab studies on impact of sitting at SoC and temperature floating around somewhere for generic lithium batteries.

Great post.

 

[sdorn]

I have never even been in a Leaf, but I have heard they have more battery degradation than Teslas have had. I know Nissan had to replace the batteries in some early Leafs under warranty because of severe degradation. It's possible Nissan has some circuitry in there that makes charging to 100% impossible and the reported capacity is only the usable capacity. The current 60 KWh battery from Tesla is essentially like this.

This article goes into the technical details of what happens charging Li-ion batteries to 100% as well as a number of other charging scenarios
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

I normally charge to 90% and have only charged to 100% once, though I charged to 95% a couple of times on a recent road trip. For most driving situations, you don't really need more than 90% on a day to day basis. It's rare my car is ever below 200 miles of range remaining.

That is a good article. It says the optimum charge level for longevity is 3.92v/cell and a 100% charge is 4.20v/cell. Does anyone know what voltage levels Tesla is using for 90% and 100% charges?

Also, the test conducted in the article for maintaining a battery at 100% charge was done over a 3 month period and it appears they actually kept the battery at the full 4.2v/cell the entire time. They did that at various temperatures ranging from 0 degrees to 60 degrees Celsius. The lower the temp, the less degradation. At 25 degrees they had 20% degradation over a 3 month period. If degradation is linear over the 3 months, it comes out to about .009% degradation per hour that the battery is continually held at 4.2v/cell.

 

[apacheguy]

90% = 4.08 V
100% = 4.2 V

 

[sdorn]

90% = 4.08 V
100% = 4.2 V

Actually, according to the blog post below back in 2006 Tesla was treating a 100% SoC as 4.15v/cell and a 90% SoC as 4.10v/cell. They also treated a battery as having a 0% charge at 3.00v/cell which they say is about a 2% SoC.

A Bit About Batteries

 

[wdolson]

That is a good article. It says the optimum charge level for longevity is 3.92v/cell and a 100% charge is 4.20v/cell. Does anyone know what voltage levels Tesla is using for 90% and 100% charges?

Also, the test conducted in the article for maintaining a battery at 100% charge was done over a 3 month period and it appears they actually kept the battery at the full 4.2v/cell the entire time. They did that at various temperatures ranging from 0 degrees to 60 degrees Celsius. The lower the temp, the less degradation. At 25 degrees they had 20% degradation over a 3 month period. If degradation is linear over the 3 months, it comes out to about .009% degradation per hour that the battery is continually held at 4.2v/cell.

Li-ion batteries are really a class of batteries that use small particles of lithium trapped in a matrix for one of the terminals and some other material for the other. The matrix is mostly graphite, though silicon can hold more ions and using a mix of graphite and a little silicon is how Tesla/Panasonic boosted the energy capacity of the cells for the 90 KWh/70KWh battery packs.

The chemistry that Tesla uses is rated at about 4.2V at max charge and the nominal voltage (the voltage the cell is for most of the discharge) is 3.6-3.7V. The exact number differs depending on the source. The actual voltage is on a curve that drops from 4-4.2V to around 3.8V quickly as the battery drops from 100% to 90%, then levels out and drops slowly from 90% to about 10% from about 3.8V to around 3.4V, then it drops off a cliff at the end.

Ultimately it isn't the voltage that you want to be most concerned about, the voltage is mostly determined by the electromotive potential of the materials used for the anode and cathode. Lithium is always one pole with a li-ion battery, but the other depends on the chemistry chosen. Different chemistries have different characteristics. Some have higher energy storage (higher Ah ratings), but are more prone to fire for example. Tesla uses the highest energy density chemistry, but it is more prone to fire. They go to great lengths to keep the batteries out of the danger zone.

I wrote more about battery tech here:
Battery Tech Part 2 | Tesla Blitherings

 

[wdolson]

Actually, according to the blog post below Tesla treats a 100% SoC as 4.15v/cell and a 90% SoC as 4.10v/cell. They are limiting us from ever actually charging to 100% in order to prolong battery life. They also treat a battery as having a 0% charge at 3.00v/cell which they say is about a 2% SoC.

A Bit About Batteries

Most of the curves I've seen show the voltage is more like 3.8-3.9V at 90%, but Tesla has worked with them more than I have (and just about any other user of Li-ion batteries).

Li-ion batteries don't like to be at 100% nor do they like being at 0% charge. Both can damage the battery, so considering the battery as "empty" before it actually reaches zero is good engineering.

Tesla doesn't get the credit they deserve for their battery management software. I've done a lot of work on embedded systems (microprocessors that run on something inside a system and you don't have direct access to it like you do with a computer running Windows, MacOS, Android, iOS, etc.) over the years, most have had some kind of AC power source, but working with a battery powered system has all sorts of headaches the programmers and hardware engineers need to consider. For one, how do you deal with a low power situation and dealing with a 100% charge situation can be a headache too. At 100% charge a system has more voltage than it does during most of its operation.

Managing the battery over the entire range of charge is kind of an art form. In the cell phone world (and other portable devices) I've noticed Apple tends to be better at this than most of the Android makers, but Tesla is outstanding at it, better than Apple IMO. With a typical laptop, or cell phone you are seeing serious battery degradation after a year or two most of the time, but there are people with Model Ss with over 100K miles that have only seen a 5% degradation. In almost 6000 miles my car has seen 0%.

 

[Hugh Mannity]

Your 2015 Leaf doesn't have a 80% charge setting? Weird, my 2013 did. Maybe your 100% isn't a full charge but a 90%ish so you are good to fully charge all the time?

 

[apacheguy]

Actually, according to the blog post below back in 2006 Tesla was treating a 100% SoC as 4.15v/cell and a 90% SoC as 4.10v/cell. They also treated a battery as having a 0% charge at 3.00v/cell which they say is about a 2% SoC.

A Bit About Batteries

Well that was 2006. It's different now. I'm pulling my numbers directly from CAN.

 

[apacheguy]

Your 2015 Leaf doesn't have a 80% charge setting? Weird, my 2013 did. Maybe your 100% isn't a full charge but a 90%ish so you are good to fully charge all the time?

Nissan, in their infinite wisdom, eliminated the ability to charge to less than 100%.

 

[sdorn]

Your 2015 Leaf doesn't have a 80% charge setting? Weird, my 2013 did. Maybe your 100% isn't a full charge but a 90%ish so you are good to fully charge all the time?

No, there are no charge settings. It always shows 100% when it finishes charging.

 

[mspohr]

One data point is the Tesloop limousine service which runs between LA and Las Vegas daily. They have an S 85D and Supercharge it to 100% daily. They've put on 200,000 miles in one year and only noted 6% battery degradation.
Impressive.