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40kwh Battery Degradation?

Has there been any official information about how battery degradation works on the software limited 60kwh battery? For example, if the software limits the battery to 2/3 of the capacity of the battery, there will be degradation. If the software limits to 40kwh, there should be no degradation.

At best there are perhaps 500 S40's out there, and you are asking about a question 8 years in the future. If I had to guess though, I would say hitting the upper and lower limits of the battery pack is balanced against the more frequent charging cycles you'll need with a 40. Guess is it's a wash, but you should not have an issue.

The 40 is software limited to charge to a maximum of 72% of capacity of the 60 kWh pack.

Capacity is a number that gets recalculated over time, as the battery ages. So 72% of a number that declines slightly with time will reduce in pretty much the same manner as the 60.

This is really not an issue though.

Roadster capacity has been shown to be 90-95% capacity after 50,000 - 100,000 miles.

Model S battery pack is more sophisticated and will certainly outperform the roadster.

The limit of 72% will further extend life relative to a 60 that is charged to 90%. This means that the 40 will be a very stiff pack that will show very little reduction over time.

The main foible of the 40 was the limited range, which the market voted was not enough for most people.

For those with a lifestyle that fits the short range, it's fine (like my wife). But for everyone else, the 60 or 85 are better.

Hi Mark,

I'm not sure if we know it is 72% of the actual current (recalculated capacity) or 72% of the rated capacity. It is possible that our rated range, might decrease at 71% of rated capacity. But like jbunn says, we might not know for a few years.

Additionally, since the 40 only charges to 72%, (however that is calculated) the degredation will be reduced as compared to charging it to full. So you have that going for you.

My car charged to 144 consistently when I got it, and now hits 139, after 3000 miles. Let's hope that's not a pattern.

My 40 did exactly the same thing.

Then the battery failed and was replaced.

The new pattern was a full Rated charge of 147, with degradation to 142 in about two weeks.

Now a new pattern has emerged. Actual and Rated mileage have become much closer since the last firmware upgrade. For example, today my 10-mile drive used 9.5 of Rated range. That's been the case for several days and I'm not sure why. I suspect the range algorithm has improved but haven't observed it long enough to be sure. Has anyone else seen this behavior?

This weekend when I started out, I had a rated range of 135, but went 11 miles before it dropped to 134. First time that I saw that. Running version .61.

The software needs to be updated to trickle charge the battery and keep the batter at full charge. The vampire drain eats up to many miles when sitting over night. Trying to top off the battery of the missing 5 or 10 miles seems to never get the charge back up into the 140s.

It would be very surprising if they kept us software locked after a year or two. It's not worth the cost of maintaining the software for so few cars.

+10,000 murraypetera

@murraypetera +13500

My 40 at delivery was rated range 147 , May 29, today its down to 139.

Mine finishes charging about 5 minutes before I leave for work, so it's not vampire drain. But I've definitely seen the car go several miles before the range downticks, so it could be algorithm.

Topping off seems to hit around the same 139. My typical day leaves me with about 45 miles to spare, so it's no big deal. If I end the year with a range in the 120's after charging, there will probably be some phone calls.

And what happens if we decide to upgrade to the full 60 3 or 4 years down the road? Do we pay full price, or will the cost be prorated?

I currently live in Seattle area where 120-130 miles of range is fine for me except maybe 4 or 5 trips a year. However, I'll be moving to Southern California in about a month. There, a trip to the supermarket with a couple of side trips could take you over 120 miles. I'm wondering whether I'd be better off upgrading or selling and buying a new car.

Also, anyone have any suggestions on sending my 40 down to San Diego? Can't drive it, so I have to send it down.

Murray, I really doubt that there is that much coding involved in creating a modified artificial limit to charging (Tesla already puts a cap on all MS batteries to reduce degredation, so it is just a matter of changing that cap and I can't see that as a hardship.

By "upgrading" the 40's to 60's Tesla loses the possibility of future revenue.

I've read that the issue is re-balancing. In my case I have seen it show full charge at something around 141 as opposed to the 145 it used to show then I drove it down to near 0 and the next charge went back up to 144. I've also read that if you charge at a slower rate it shows a higher number when you're done so I wouldn't jump to conclusions about battery degradation just yet.

@chicagoniner
Same here. My 40 had been charging to around 142. Then on Saturday I drove it to Zero and it charged to 147 again. I'll try this again next month.
I wonder if the battery changes, or reaching Zero just helps the algorithm somehow.

Interesting point @chicagoniner. I've never gotten mine below 20 miles range remaining, and I always charge at 40A.

After a few years of 40 degradation, does upgrading to a 60 give the full capacity of a new 60?

Update...after another month, I was consistently hitting 138, and then 137. I tried running the car down to 15 miles left, then fully recharging and that made no difference. Charging at 30A and 40A had the same result, as did the HPWC and Roadster charger. Then this morning I came out and saw 140, which was after a top off from 100 at 40A, so I'm thinking it was probably higher than that when it completed. I hadn't seen 140 in months. It was slightly cooler last night in the garage (95 degrees instead of ~108), maybe I'll try charging it with the garage AC running. Basically this looks like it's going to be heat related, and hopefully it springs back to the mid 140's as the weather cools down in Phoenix.

70-75*F will be where you see about the best range. For any EV. Can you open a window and vent the garage at night somehow?

I see at times an 8 mile variation and I think its vampire loss. I still have 4.5. I have an 85 and charge to different levels. Of late I have been charging to the level that gives me around 200-201 yet this am it was 194. Last night I was fully charged up to 200 at 8pm. if you need those extra few mile I would suggest unplugging and reinserting your charger about 20-30 mins before you leave and you will get your miles back. Otherwise perhaps wait for 5.0.

so, just a thought here, i don't think anyone here is experiencing battery degradation -- the idea that at T1, you could charge to X and at T2 you could only charge to X-5 ( a few miles less ) does not mean that there has been any battery degradation. That is the software and the computer giving you a different range estimate. In order to see battery degradation, you would, at minimum, have to be able to see the actually kWh storage in the car battery.

Here is my MS(40kWh) gives me. Just for reference.

First month, driving average 330 wh/mile, estimated range 143 miles when fully charge.
Second month, driving average 320 wh/mile, estimated range 140 miles when fully charge.
Third month, driving average 317 wh/mile, estimated range 137 miles when fully charge.
Fourth month (now), driving average 315 wh/mile, estimated range 134 miles when fully charge.

6000 miles on my 40. Was charging to 142 when I received the car and is now charging to 139. Charging mostly at 30 amps. Car has been driven down to 6 miles with no noted effects. I was led to believe that the degradation would be at the top end and not apparent to 40 owners. I hope the range does not continue this downward trend but it makes sense that the scenario which calculates 72% of battery capacity would result in an incentive for 40s to pay for the upgrade. Not sure what is reality at this point.

@vincent1001, that was exactly my trend up until now. I had a gradual mile by mile decrease over the first three months, never deviating up, only down. I've probably charged the car 75 times and this was the first time it was higher than the last. All despite being more sensible driver with lower Wh/mi. I'm charging at work right now in the desert sun, and it looks like I'll be back to 137 based on what the app is showing with 30min remaining.

I’ve been driving my 40 for over 4 months. Full charge started at 147 but soon fell to about 140 and has been steady at this level. Of course, I live in the cooler temps of S. California.

I think Tesla will eventually prorate the cost of upgrading to a 60. The battery depreciates in value and in charge capacity over time so asking full price makes no sense. I figure that there are 1000 40’s on the road (pure guess) so that is about $10 million in revenue that Tesla is leaving on the table. I’m hoping that after a year of the last 40 being delivered, they offer us 40’s a “deal” to upgrade. Waiting a year will assuage those who paid more for a 60 kWh and it will help Tesla justify the reason for a lower upgrade price.

My 40 started with 143 miles, now it is down to 137 miles after 5 months. Sometimes it even only charges to 134 miles.

In lithium ion batteries it is necessary to full charge once in a while for the battery to know its capcity.
Here is what I am wondering about. If the 40kwh battery is limited by charging to 72% capacity, how does the car know what is its 100% capacity if it never charges to it? This could be what is causing the range degradation for the 40kwh battery.

Started with 145, now I'm down to 133. It's basically a straight line down. I thought cooler weather would make a difference, but it hasn't (although Wh/mi has come down a lot). Even at 300Wh/mi I'm lucky to get 115 miles on a charge due to vampire on 4.5. Still not a huge deal since the most I ever drive in a day is ~70 miles. Tesla checked my battery at the service center and said all is well.

I am down at 133 too ,, and some mornings hits 134. Early morning temperatures 62-65 degrees

Are you guys looking at ideal range at max charge and comparing the same versions of firmware? There has been changes in rated range calculations. I had my rated range calculation change overnight and many others saw the same after one of the updates.

The old regular charge was to 93% but the slider is now in 10% increments. I think they may be hiding more range for reserve because some people were pushing it beyond zero intentionally. Not sure about that but it may be the case.


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