Jeff Dahn's recommendation on long term battery preservation

[Roadster2010]

Ah, good point on battery cooling, @BartJ.
I assume that on Storage charging, the current level is low enough that battery heating is not an issue?

 

[Roadster2010]

By the way, how do I set my car to charge to 70%?

 

[FlatSix911]

How often should the battery be charged to 100% for rebalancing?

 

[Snowstorm]

By the way, how do I set my car to charge to 70%?

You scan do it from the phone app or through the touch screen. Tap the lighting bolt icon near the top and then set charge limit. Use slider or arrow buttons to change.

Degradation is function of temp and charge level (hot is bad). I used to charge my 100d to 70% in the summer, but now that it is below 0, I charge to 80% to give me buffer for heating and snow.

 

[Roadster2010]

Thanks @Snowstorm.
Ah, I hate to show more ignorance, but ... there's a phone app for the Roadster??

 

[Brass Guy]

"Fast" and "slow" are relative terms.

Supercharging is fast. Up to 120kw. (Requires cooling, even in cool weather.)
L1 (120V) charging is slow, around 1.4kw. (Cannot even keep up with the battery heater.)

I doubt the difference between 240V at 40A and at 72A (9.6kw-17kw) would make a noticeable difference over the life of the car.
The biggest concern over charging rates in this range is efficiency of the equipment and wiring involved.

From everything I've read so far, the best you can do for your battery is keep it from extremes. Including temperature, charging-discharging rates, and SOC.

I plan to keep mine for a couple of decades too. Should be a half million miles by then. If I can still see well enough to drive.

 

[Snowstorm]

Thanks @Snowstorm.
Ah, I hate to show more ignorance, but ... there's a phone app for the Roadster??

Sorry I had no experience with the roadster. I was referring to the model S cira 2017

 

[dhrivnak]

I'm more interested in how FAST to charge my 2010 Roadster.
I've seen all kinds of comments, but I'm still unsure if it's better to charge slowly or quickly (i.e., lower or higher amperage).
Are there expert opinions on charging rate?

According to Tom Saxton 32 amps is the sweet spot. Faster or slower we have higher losses. And 32 amps is better for the utility as it is a more stable power flow. Then as an engineer virtually everything lasts longer under light use.

 

[Roadster2010]

Thanks @dhrivnak. There seems to be a general acceptance of 32A as the way to go.

 

[seclinton]

Thanks @dhrivnak. There seems to be a general acceptance of 32A as the way to go.

32A is just 25% margin on a 40A circuit.

Charging batteries runs CCCV again if I am wrong below, please help me correct it.

Constant current up to a certain point, then switch to constant voltage; current will taper down. 100% SOC is when -Delta V is ~20MV. You’d see this in a battery charge/discharge plot.

 

[nrechtman]

I decided to do a video on this as it's a fairly common question I've come across and hard not to get several different answers. So, I reached out to Jeff Dahn (Tesla Industrial Research Chair and Professor of Physics and Atmospheric Science at the University of Dalhousie in Nova Scotia). I advised I was planning to keep my X for approximately 2 decades and asked him where he'd charge the battery to for day-to-day use, with long term preservation in mind.

Check it out here:



For those that don't wish to watch the video he recommends daily charging to 70 percent and to go ahead and charge to 100 percent for longer trips. He also comments on Vancouver being a nice climate for lithium ion batteries. Cheers.

Your link is gone

 

[FlatSix911]

Tesla battery expert recommends daily charging limit to optimize durability
.
Historical data from Tesla’s current battery packs show about 5% capacity degradation after 50,000 miles (80,000 km) and the capacity levels off for about 150,000 more miles before coming close to hitting 90% capacity. Therefore, they are already doing well and could last for years and hundreds of thousands of miles, but there are also things that you can do to optimize the results.

One of those things is not charging to a full charge too often. Repeated full charges can negatively impact li-ion battery cells, which is why Tesla recommends to only daily charge to 90% capacity and to charge to 100% only when needed for long trips. In the past, CEO Elon Musk even recommended 80% daily charging... Both are easily manageable in Tesla vehicles since they all offer over 200 miles of range on a full charge and therefore, they can cover most daily commutes with even just a fraction of a full charge. But if someone wants to really push the optimization to its limit, Dahn suggests going even lower. A Model X owner on TMC aims to keep his all-electric SUV for up to 20 years and he decided to reach to Dahn for advice on daily charging to optimize the battery pack longevity. The researcher responded:

“I would recommend charging to 70% normally. When you need a long trip, charge to 100%.” That’s even lower, but again, it’s still over 150 miles of range on most versions of Tesla’s vehicles and if the need arises, they can actually charge to 100%.

 

[Snowstorm]

The other issue is how much you discharge it. From what I know, it is not good for Li Ion battery to deeply discharge them. So you should not go past 10% and ideally not below 25%. This means that if you charge to 70% and discharge to 25%, then only 45% total range is achieved. Good enough for most commute still.

 

[Amit519]

We have just bought a house (try to settle down?!) in Blacksburg VA. I asked electrician to install a Tesla Charger he suggested that the wiring difference between 40Amp (available) and 80A is around $150. I wasn't going to spend the extra as overnight charging would be the same.....

Does anyone know if it is better to charge more slowly? If I had the faster charger, I could keep the charge limit lower and have the option to top it off quickly. Any thoughts?

Hi @bcalfee,
$150 is not a big difference but the faster charging will be appreciated in the rare case you depleted the battery and need to turn around and make another trip. If it's not too much more, it would also be a good idea to install a breaker box and plan for a second charger daisy chained later. Trust me, you may find yourself buying another Tesla in the future and will regret not running the 100A line and a breaker box. We bought 2 Tesla Model S cars 45 days apart, it was a no-brainer to own a Tesla after buying our first one.
As for charging rate, you can always set the limit. I have been using the Tesla superchargers almost exclusively and have no worries about battery degradation, at least for the next decade of ownership before any battery life is impacted.
Hope this helps,
Amit519

 

[CHGolferJim]

There is no substantiated answer to the question? Is the break on the sliding scale shown on the UI at 90% just a vague indicator between “daily” and “trip” charging? I almost always charge at home to 85% and keep plugged in constantly, and up to [120% of next leg mileage shown on NAV + 30] on trips. When departing on trips, I set it to 100% to finish within an hour of departure since I generally have a longer first leg of 130-150 actual miles. So far, at 54k elapsed mileage over exactly 3 years, my 100% is 230 vs. the original 240 = 4% loss. I am hoping to be able to do a battery replacement by 2025, if I haven’t changed over to a Model Y.

 

[shred86]

Any recommendations from Jeff Dahn if the car won’t be driven for an extended period of time, perhaps a month or longer? Many folks recommend 50% state of charge but I’m not exactly sure as to the reasoning other than it’s the lowest setting you can choose on the app for keeping a vehicle plugged in. I can’t seem to find it anymore but there was a chart that showed the difference from 20% to 100% SOC and the impact on battery degradation but I can’t seem to find it. I just remember it showing 20% has the least impact on battery degradation.

 

[shred86]

The articles "How to Store Batteries" and "How to Charge and When to Charge?" at Battery University recommend 40-50% state of charge (actual battery capacity, not necessarily what's displayed in the Tesla, although I think it's fairly close) for long term storage. According to the article, this "minimizes age-related capacity loss while keeping the battery operational and allowing for some self-discharge." It also has some good data on how higher temperatures will further degrade your battery, which is fairly common knowledge but it's good to see some actual numbers.

The articles "How to Prolong Lithium-based Batteries" and "What Causes Li-ion to Die?" provide some great data that recommends two key points: 1) a cell voltage of 3.92V appears neutral, lower voltages add to solid electrolyte interface (SEI), higher to electrolyte oxidation (EO). Simply, the stuff that causes lithium-ion batteries to degrade. 2) Smaller depths of discharge (DOD) is better than bigger DOD. The 3.92V SOC seems fairly close to Jeff Dahn's recommendation of 70%, although the exact cell voltage will vary on the model and battery pack but it's got to be within +/-5 to 10%. The smaller DOD also aligns with the user manual where it states, "There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly." It's also worth mentioning the user manual, in capital letters, says to leave your vehicle plugged in, which also makes sense to help reduce vampire drain and maintain optimal battery temperatures.

Some other random things I've learned watching videos is a 100% SOC displayed in a Tesla (85 kWh battery) is ~4.2V and 0% SOC displayed is ~3.0V, which seems to be fairly typical for devices that uses lithium-ion batteries. Those displayed percentages can sometimes be off if the cell packs become "unbalanced". There's several examples of Tesla's shutting down with >0% displayed SOC, when normally there's a buffer below the displayed 0%. I do think the term "unbalanced" is a little misleading because everything I've seen from folks reading the CAN bus data shows the Tesla BMS does an excellent job of keeping the cell pack voltages balanced. It really just seems the displayed percentage can become out-of-sync a bit and when folks mention this idea of "balancing" the cells (discharge close to 0% and fully charge up to 100%, three times), it's really just normalizing the displayed percentage again with how it's intended to be. There was a video of one guy who saw a decent voltage difference with one of his cell packs but even after trying to follow the "balancing" procedures mentioned above, it was still the same. I suspect in his case that cell pack is just degrading quicker than the rest, and there's nothing you can really do about it.

It's been very interesting learning about this stuff and what folks like Jeff Dahn, Tesla and others in the battery industry are doing is really impressive. As far as charging your vehicle, it's pretty clear following Tesla's simple recommendation mitigates what was mentioned above to easily get to a life cycle of 8+ years.

• Keep it plugged in and charge daily.
• For daily use, charge somewhere between 50-90%.
• For long range trips, charge >90% if needed and try to minimize how long the SOC is >90%.
• For long term storage, charge to 50%.

If you have no idea what to choose between 50-90% for daily charging, 70% appears to be a great setting based on Jeff Dahn's recommendation (seems like he knows what he's doing, lol). You can (and should) easily adjust this based on your usage. For example, I average about 12% battery use for my commute to and from work. I have such a large buffer with even 60% SOC that I find this setting is perfectly suitable for me (and it appears to be close to 3.92V and what @seclinton mentioned in this thread). If I was averaging something like 50% battery use for my commute, I would charge to something like 80-90% to have the extra range as a buffer because I personally like the idea of having plenty of extra range in case something comes up and I can't get to a charger. Anecdotal data shows there's very little difference with charge levels between 50-90%, at least for the period of time we have data for ~1825 days (vehicle age), ~800 cycles and ~250,000 km. Perhaps in another 5-10 years if we're still collecting that data on the same vehicles, we might start to see a small but noticeable difference in degradation from say Tesla's that used a 60% SOC versus 90% daily. However, there's so many other variables to consider and it's using displayed range to make comparisons that I'm more inclined to look at what the scientific data shows (which, as of now, seems to align with the anecdotal data for the most part).

One thing that still confuses me is there's still some data that suggest even lower SOC is actually better (again, we're talking very small benefits here) in terms of reducing battery degradation. JB Straubel at one point mentioned 50-62% and some articles seem to suggest even lower would be better, so I'm not sure how that compares with the cell voltage of 3.92 mentioned above. @seclinton, would love your expertise here if you're still around.

 

[shred86]

I finally got TM-Spy up and running recently. After charging up to 70%, I checked the voltage of the battery cells and sure enough, they're sitting at ~3.92V (see attached screenshot). So it does appear that Jeff Dahn's recommendation aligns with the articles from BatteryUniversity.com that I posted above.

Of note, the screenshot below shows my SOC at 71.6% which is the actual SOC. The displayed SOC in the vehicle was 70%. There's a buffer so when you get to 0% displayed, there's still a little bit of charge left before the car shuts down. I've seen this closer to +3-4% in the past, so it's strange I'm only seeing a +1.6% difference. I think it may fluctuate depending on the SOC. As long as it's not the opposite (actual SOC is lower than displayed SOC), I'm happy with it.

 

[TMThree]

3) Deep discharges should be avoided.

What is a "deep discharge"? The depth of the discharge or how far down you went? i.e; dropping 50% worse than dropping to a low % voltage remaining?

 

[Snowstorm]

What is a "deep discharge"? The depth of the discharge or how far down you went? i.e; dropping 50% worse than dropping to a low % voltage remaining?

Don’t go below 20% everyday. Seriously though, use your battery as you have to. Yes, full charge and deep discharge is bad, but it is more like eatting a Big Mac for your health, not an issue unless it is all you eat everyday.