Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health

[Krazaak]

I got a reply from my local SC adviser and am probably more confused now than before. He reports my battery is fine but that my battery is showing low because I don't discharge the battery to 20% before plugging it back in.

Huh?

I thought "a plugged in Tesla is a happy Tesla".

I get the impression that something is screwy with the Model 3 BMS in some cars and I'm not sure Tesla actually knows (or just isn't sharing) what's getting it out of sync. Some people need to drain and recharge to keep the BMS from getting out of whack and others have seemingly no issues. My Model X I've recharged nightly to 90% for 3 years and it shows little degradation, 2% or so, charges to 285 (out of 289 P100D) rated. My wife's Model 3, goes a few weeks of getting charged to 90% once or twice a week after being driven down to 30% and then goes a week or two getting 90% nightly charges when it's driven more frequently but only down to 50-60% or so. It charges to 318 (out of 325 LR RWD) rated.

I think part of the problem is that people's past experience with Model S and X batteries don't apply entirely to Model 3 batteries because they're different in many ways, even within the S and X models, 85kWh, 90kWh and 100kWh packs degrade differently.

There's barely 2 years of data on what's "normal" for the Model 3 and there seem to be pretty different experiences between owners.

If you feel like doing a little research, take a look at the service bulletins (manufacturer's communications) on the NHTSA site, down at the bottom of the page, specifically the electrical ones and look for any battery related ones that fall within the manufacturing timeline for your vehicle.

2018 TESLA MODEL 3 4 DR AWD

You'll have to open the document for each one individually to find ones specific to your month of manufacture and I imagine you'll have to deal with Tesla to get the actual day and potentially run the VIN. Tesla stating your battery is fine might just mean you're not on any list of affected VINs or might mean they've looked at battery information. It could also mean they've actually done nothing and just told you it's fine because it's below 30% and they're just hoping you go away for now.

 

[astrowunder]

I bought my LR AWD is Oct of last year and we saw some decrease on the Stats app (305 miles) through the first 7k miles of use in Oct through March, the colder months. Then, in April from about 7k-9k miles I was back at 308-309 range. At the 9k mark in mid-June, after installing one of the 2019.20.x firmware updates, my range dropped to about 300 and has been trending downward since. I'd expect a lower range algo if my wh/mi figures were poor as they are in winter, but not in the summer where I'm averaging 225wh/mi or so.

I realize this is obviously not the end of the world, but I relate this to a suspected oil or headgasket leak on a gas car. Is there a real problem and is it going to get worse? Not having real information is frustrating. I can check for an oil leak, I can't check for real battery degredation. We have two Teslas and my wife drives much more than I do so she often charges in the garage on weekdays. Prior to the June update and now v10, I could charge to 80% on Sunday night and not have to charge my car again until the following weekend. Now, between real/imagined range loss and some of the phantom drain I've experienced with v10, I'm back to changing my charging habits so that I charge almost daily with a lot of car swapping at night and in the morning.

I've seen nearly the same. My first 15k I had 306-307. Sometime this summer it suddenly dropped to 297. Hoping it's just an algorithm goof.

 

[astrowunder]

My bigger question is what happens when you 'use up' the 260 or whatever and the estimate shows close to 0? Do we really have another 50 miles that it's just not telling us about?

 

[voip-ninja]

My bigger question is what happens when you 'use up' the 260 or whatever and the estimate shows close to 0? Do we really have another 50 miles that it's just not telling us about?

thats my issue too.

 

[AlanSubie4Life]

Since the energy graph consistently shows my estimated range at even less than the display range I am left to conclude that the range loss in my car is real

The value of the estimated range (not the battery gauge) is easy to calculate:

For your LR DM, it's:

Remaining rated miles * 245Wh/rmi /(Efficiency over last 5/15/30)

So for example if you had 150 rated miles left, and you had selected efficiency averaged over the last 30 miles, and that was 270Wh/mi on the trip meter:

150rmi * 245Wh/rmi / (270Wh/mi) = 136 miles would be what the range predictor would predict.

You can check this yourself fairly easily.

Note, however, that this projection is slightly optimistic - your rated miles will actually click off a little faster than the range predictor would suggest (they click off at one rated mile per 230Wh used).

So your actual range (to zero rated miles) is 150rmi * 230Wh/rmi / 270Wh/mi = 127 miles

I don't know why this discrepancy exists - there is a reserve, so you certainly can go further than 127 miles, but the scaling is not correct (in spite of the wierd scaling, for very low remaining range it should be pessimistic, but for very high remaining range it will be way too optimistic). For example, in the case of 20 rated miles remaining vs. 200:

20 *245/270 = 18 miles (You can likely travel further than this at this 270Wh/mi efficiency, due to the reserve.)
vs. 20*230/270 = 17 miles (actual miles to travel at 270Wh/mi to get to 0 rated miles)

200*245/270 = 181 miles (Even with the reserve you likely cannot travel this far at this 270Wh/mi efficiency).
vs. 200*230/270 = 170 miles (actual miles to travel at 270Wh/mi to get to 0 rated miles)

 

[GregD60]

My bigger question is what happens when you 'use up' the 260 or whatever and the estimate shows close to 0? Do we really have another 50 miles that it's just not telling us about?

Good question. Who wants to be the guinea pig?

 

[Krazaak]

due to the reserve

What reserve?

 

[StellarRat]

What reserve?

The battery probably does have enough power to go more miles, but the software will shutdown the car to prevent damage from over discharging it. All EVs (as far as I know) have both a top and bottom buffer/reserve to prolong battery life. From my reading maintaining a mid-level amount of power in the batteries lengthens their life by something like 3x - 4x. You wouldn't want an EV that was true 100% - 0% capable.

 

[AlanSubie4Life]

What reserve?

According to Elon (see several tweets), there is a reserve below 0 rated miles (if the BMS is working correctly). Would not count on it...

In addition if you look at the EPA discharge event in conjunction with the measured discharges, it does seem to imply there are a couple extra kWh below zero.

 

[Krazaak]

The battery probably does have enough power to go more miles, but the software will shutdown the car to prevent damage from over discharging it. All EVs (as far as I know) have both a top and bottom buffer/reserve to prolong battery life. From my reading maintaining a mid-level amount of power in the batteries lengthens their life by something like 3x - 4x. You wouldn't want an EV that was true 100% - 0% capable.

All the models have a buffer, a buffer isn't a reserve. The buffer is there for the very reason you state, which is to prevent the batteries from being damaged by a complete drain. You can not drive into the buffer.

 

[StellarRat]

My friend drove hers until it said 0 miles then she went another mile or two maybe that's the "reserve"??

 

[ElectricOrgan]

My friend drove hers until it said 0 miles then she went another mile or two maybe that's the "reserve"??

I seriously doubt it. I remember a video by Bjørn Nyland (I think) where he drives his car until it stopped. He wasn't able to drive over 25 (km/h? m/h?) until he got to the charger. I don't recall if it was on zero the whole time or not. In another video the car said he had 14 km to go and he was only a couple of km from the Supercharger when it quit. After sitting for a while the range changed to zero and he still couldn't move the car.

So much for driving on reserve. I think if you can drive while on zero, it is because the number being reported isn't the same as the info they use to shut down for protection. Likely the shutdown happens when any one of the many cells reports that it has individually reached the cutoff point which may not coincide exactly with the aggregate range estimate.

 

[Krazaak]

My friend drove hers until it said 0 miles then she went another mile or two maybe that's the "reserve"??

Battery capacity is always a little bit of an estimate. How far you can go past 0 depends on how accurately the BMS determined capacity and how balanced the pack was. If you drive slow enough you can you can draw out a little more juice before you hit the critical threshold in a module that shuts the whole pack down.

I've seen enough reports of people shutting down exactly at zero, a little before or a little after to believe there's a true reserve capacity. In the race to claim longest range, why would you leave miles on the table and not document the reserve?

I've seen Elon's tweet about the reserve, I simply don't believe it is accurate as interpreted. There's a buffer that keeps the battery from being damaged when it reaches 0%, but that buffer isn't usable or it wouldn't serve as an actual buffer.

If there's both a buffer and a reserve (that can be reliably counted upon), I'd be curious to see actual supporting evidence. 10-15 miles could be 3-4kWh, that's a lot of reserve in addition to the buffer.

 

[StellarRat]

I seriously doubt it. I think if you can drive while on zero, it is because the number being reported isn't the same as the info they use to shut down for protection.

She only went a mile she said. That's really not too far past zero. Hard to say, but I have no reason to believe she'd make that up.

 

[Krazaak]

She only went a mile she said. That's really not too far past zero. Hard to say, but I have no reason to believe she'd make that up.

I don't doubt it. On a 300+ mile range car, 1 mile is a rounding error.

 

[ElectricOrgan]

She only went a mile she said. That's really not too far past zero. Hard to say, but I have no reason to believe she'd make that up.

Then there is the fact that the number displayed is an integer that is rounded off in the calculations. So figure when it first reads zero it is actually 0.5 per cent or miles then that means you have a bit further to go until it actually reaches true zero, half a mile, half a percent, pick one.

 

[AlanSubie4Life]

Then there is the fact that the number displayed is an integer that is rounded off in the calculations. So figure when it first reads zero it is actually 0.5 per cent or miles then that means you have a bit further to go until it actually reaches true zero, half a mile, half a percent, pick one.

I’m a bit surprised that no one has tested this on a dyno.

Remember in the EPA test they managed to pull 79.2kWh from a battery with 4000 miles on it. The EPA depleting test I think runs at a pretty low power at the end though (can’t remember). So our cars should be able to do that, but you’re not likely to be able to drive freeway speeds when you are anywhere near the reserve/buffer.

Notably, 310 rmi * 245Wh/rmi is only 76kWh...so where is the other 3.2kWh?

In any case I agree it is not something you’d ever really want to test outside of a controlled environment. There are people here who have routinely reported driving to zero miles though. @Nate977p if I recall...I wonder if he has ever dipped into the reserve?

 

[bigroccrek]

Tried re-balancing the battery pack (ran battery % below 20% and then charged to 100% and left plugged in for additional 7 hours) based on what I read on various forums. charged to 286 miles at 100%. Ran down to 20% again and then charged to 100% again and range was 290. Still seeing a 5% reduction in battery capacity/range. Dissappointed.......

 

[nvx1977]

i'm getting 262mi charging to 80%. this is actually higher since around the initial v10 release. Used to be in the ~250mi vicinity. I have an LR RWD.

 

[T3SLAROD]

Same here and I am trying hard to not worry about it, 2018 LR RWD started at 290, 285, 280, and after this update 276 , this morning 272.

I have a feeling that the true safe everyday 90% for this car is 250-260 miles with no degradation after.