Charge to 90% or 80% daily?

[Tam]

Why doesn't Tesla just state this clearly in the manual? I am shocked that after all these years they still do not have anything in there about the "best" for "recommended" levels.

It's possible that the technology, the chemistry recipe is still evolving, the target keeps on moving and it is still new to get enough data.

Thus, although there's no precise number, we do get a range of 50 to 90% daily settings.

 

[KenC]

Agree!

It's very clear that we should not worry about the health of the battery as long as we stick to the above parameters.

The 90% charge coming from Tesla Service Center is because owners keep complaining that they keep "losing" miles and their batteries keep "degrading" (It's just a more prominent calculation drift for sub 90% setting that has no effect on the battery real range).

90% charge is to minimize the calculation drifting and it has nothing to do with whether 90% is drastically healthier or worse than 50%.

Perhaps, not "drastically healthier or worse", but there must be a difference, otherwise, why offer a range at all? Why not just show 90% as the daily SOC charge limit and leave it at that? Simple concept for owners to understand, like keeping a full tank of fuel.

By showing a daily charge range down to 50%, kind of implies that there may be a reason for an owner to choose a SOC level as low as 50%, and what is that reason? Obviously, the Tesla battery is similar to other batteries that use lithium chemistry and that a charging range close to 50% is the best for battery longevity. The difference might be marginal, but it exists, otherwise, why give the owner a choice at all?

 

[Tam]

...The difference might be marginal, but it exists...

No argument from me that there must be one number that is better than another but my guess is for most people, the difference is not drastic enough over the life of the car to worth the hassle.

 

[Gizmo35]

I was charging to 80% since I got the car and switched to 90% about 2 weeks ago for no real reason other than to give the car a chance to balance the pack. I can get away with charging to 50% daily since my commute is around 40 miles round trip. But should I? That is the question.

 

[vickh]

It says clearly "the true range is not affected".

So its just the guage temporary "loss".

The only real physical permanent damage happens below 5% SOC right?

 

[smatthew]

I charge to 90% pretty much every day, but only finish charging right before I leave, so the car typically spends < 1 hour at 90%, then sits at ~80% for 7 hours and ~70% or less for ~16 hours. I'm on my second Tesla over the last 5 years and both cars actually gained a small bit of range from when I picked them up. My current car shows a rated range increase of 0.25% after 12000km.

I have seen temporary drops in range when I have left the car sit for a week or more at 50%, but the range comes back in a few weeks of daily charging.

Point is, by charging right before you leave, you can get the best of both worlds - the BMS doesn't drift, the cells are balanced and the battery is not sitting at a high state of charge for a long period of time. I also never charge when the battery is cold. If I have to park outside in the winter and charge, I warm the battery first. I also reduce the charge or run the battery cycle deeper on really hot days to avoid high SOC & temp.

My Model S Teslafi chart - the dips are from when I leave the car sit at a low charge (50-60%) for a few days or more. The peaks happen after a few 90% charges. The drop towards the end was from leaving the car sit for a month at 50% - took a month+ and a 100% charge to get the BMS indicated range back up (plus it was winter).

View attachment 546010

If you charge right before you leave, the cells will not balance. In order for the car to balance the cells the SOC has to be > ~85% (minimum brick voltage of 4.0 volts) , AND the car has to be asleep AND the imbalance has to be >=5mv. Keep in mind, if imbalance goes over 200mv the car cannot fix it (At 201mv imbalance, the lowest brick is 3.99 and the car will not balance unless minimum brick voltage is >=4.0 volts). It takes 24 hours of sitting there balancing the cells to fix 1mv of imbalance.

 

[Zoomit]

If you charge right before you leave, the cells will not balance. In order for the car to balance the cells the SOC has to be > ~85% (minimum brick voltage of 4.0 volts) , AND the car has to be asleep AND the imbalance has to be >=5mv. Keep in mind, if imbalance goes over 200mv the car cannot fix it (At 201mv imbalance, the lowest brick is 3.99 and the car will not balance unless minimum brick voltage is >=4.0 volts). It takes 24 hours of sitting there balancing the cells to fix 1mv of imbalance.

Since you’re being so specific, I’ll add that the car can be either in stand-by or asleep for the brick balancing to occur.

Reference: What's the power consumption of the UMC not charging?

 

[user212_nr]

So its just the guage temporary "loss".

Its not a loss at all, rather an incorrect estimate of the number of miles remaining in the battery. The number was never really accurate anyways because your actual energy usage per mile varies.

So if your have better battery health because you charged to 80% each day, then you will be able to drive farther ex. true range. Charging to 100% a few times should help the computer figure out the "estimated range" but does nothing for the battery.

The only real physical permanent damage happens below 5% SOC right?

The battery is "damaged" each time you use it, just a little bit. There is no scenario where you can ruin the battery by "going to 0" or something like that, because 0 is not really 0.

The 2 senarios that damage the battery:

1) Depth of discharge: take the amount that you discharge the battery before charging it again, and assume that it is worse go to have 1 cycle of 40% than 2 cycles of 20% even though you both times used 40%. Even if you charge correctly (as much as possible) you still accumulate damage from use.

2) Overcharging. Overcharging is counter-intuitive. The battery does not have a real 100% - the 100% is pushing the limits of the battery to the max and the battery is damaged by being in this state for a long time. So think of 90% as the real max, and 100% is 110%. Tesla could probably charge well past 100%, to the point where it would eventually explode. 100% is just the number they deem safe, but it does a lot of damage over a long time sitting in that state. In the reverse, the less the battery is charged as a total percent, the better off it is. Not exponentially, but 50 is better than 60 by a tiny amount.

 

[Fred42]

The receipt from Service Center for @Coolesnce clearly recommends changing charging habit "to 90%."

Youtuber also said Service Center told her so:

Kim at Like Tesla hasn't posted for four months. I found her videos to be watchable.

 

[user212_nr]

Kim at Like Tesla hasn't posted for four months.

Shes locked inside her home. I saw one video of a guy who did any apartment tour, "because can't do anything else".

Hard to believe its been 4 years since I first saw that channel. Back then there weren't very many such videos. I don't watch, they are too slow for me.

 

[jdw]

If you charge right before you leave, the cells will not balance. In order for the car to balance the cells the SOC has to be > ~85% (minimum brick voltage of 4.0 volts) , AND the car has to be asleep AND the imbalance has to be >=5mv. Keep in mind, if imbalance goes over 200mv the car cannot fix it (At 201mv imbalance, the lowest brick is 3.99 and the car will not balance unless minimum brick voltage is >=4.0 volts). It takes 24 hours of sitting there balancing the cells to fix 1mv of imbalance.

Not sure where you get that idea ... while it is true that balancing will not trigger until charging gets into the constant voltage curve, once triggered, balancing a) can take days and b) will continue whether sitting, driving or charging.

It's a complex and partisan issue, but discussed in depth in a number of places such as this blogpost on TMC. I'll go with wk057's opinion every time ;-)

I do charge to 95% to 100% every now and then to trigger balancing.

 

[vickh]

The 2 senarios that damage the battery:

1) Depth of discharge: take the amount that you discharge the battery before charging it again, and assume that it is worse go to have 1 cycle of 40% than 2 cycles of 20% even though you both times used 40%. Even if you charge correctly (as much as possible) you still accumulate damage from use.

2) Overcharging. Overcharging is counter-intuitive. The battery does not have a real 100% - the 100% is pushing the limits of the battery to the max and the battery is damaged by being in this state for a long time. So think of 90% as the real max, and 100% is 110%. Tesla could probably charge well past 100%, to the point where it would eventually explode. 100% is just the number they deem safe, but it does a lot of damage over a long time sitting in that state. In the reverse, the less the battery is charged as a total percent, the better off it is. Not exponentially, but 50 is better than 60 by a tiny amount.

Overcharging isn't an issue for the SR (software lock buffer) but you make an interesting point re: Depth of discharge

It is bigger % dept if you keep at 50% even for short trips. Maybe I'll keep it at 90% and will charge more as much as possible (A plugged in Tesla is a happy Telsa after all)

 

[smatthew]

Not sure where you get that idea ... while it is true that balancing will not trigger until charging gets into the constant voltage curve, once triggered, balancing a) can take days and b) will continue whether sitting, driving or charging.

It's a complex and partisan issue, but discussed in depth in a number of places such as this blogpost on TMC. I'll go with wk057's opinion every time ;-)

I do charge to 95% to 100% every now and then to trigger balancing.

Unfortunately that blogpost predates the model 3. And Tesla changed a lot in the model 3. My information comes direct from the Tesla Model 3 service manual. Not someone's opinion.

 

[smatthew]

Since you’re being so specific, I’ll add that the car can be either in stand-by or asleep for the brick balancing to occur.

Reference: What's the power consumption of the UMC not charging?

As far as the HV battery is concerned, stand-by and asleep are basically the same thing. Contactors open. No loads on the HV battery.

 

[Zoomit]

Unfortunately that blogpost predates the model 3. And Tesla changed a lot in the model 3. My information comes direct from the Tesla Model 3 service manual. Not someone's opinion.

For reference, the text in question is available from u/Wugz in this reddit thread:

Discussion on detailed info from scan my Tesla and OBDII adapter : teslamotors

 

[Zoomit]

The battery is "damaged" each time you use it, just a little bit. There is no scenario where you can ruin the battery by "going to 0" or something like that, because 0 is not really 0.

The 2 senarios that damage the battery:

1) Depth of discharge: take the amount that you discharge the battery before charging it again, and assume that it is worse go to have 1 cycle of 40% than 2 cycles of 20% even though you both times used 40%. Even if you charge correctly (as much as possible) you still accumulate damage from use.

2) Overcharging. Overcharging is counter-intuitive. The battery does not have a real 100% - the 100% is pushing the limits of the battery to the max and the battery is damaged by being in this state for a long time. So think of 90% as the real max, and 100% is 110%. Tesla could probably charge well past 100%, to the point where it would eventually explode. 100% is just the number they deem safe, but it does a lot of damage over a long time sitting in that state. In the reverse, the less the battery is charged as a total percent, the better off it is. Not exponentially, but 50 is better than 60 by a tiny amount.

You’re absolutely correct that the battery degrades however you use it, with some use scenarios more damaging than others.

The best summary I’ve seen for limiting degradation of Li-ion batteries is below from @EV-Tech Exp, which is taken from his technical and informative YouTube video that we discussed here: Battery Degradation Scientifically Explained.

It’s important to note his comments are not specific to any particular Li-ion chemistry. Where this matters most is in the quantitative suggestions about %SOC. Those values are actual battery SOC, not the indicated SOC that Tesla displays to the driver. This differs most significantly at the low end where Tesla’s 0% indicated SOC is something like 5% actual SOC. So don’t get too hung up on the numbers but the themes are valid.

Also, the perennial question is how much does this matter. How much should someone worry about possible battery degradation? The answers and opinions vary considerably. Some of us are sensitized by early EV experience, like the Spark EV I had that lost about 15% in 3 yrs and 35k mi. For a variety of reasons, that kind of degradation won’t happen in a Tesla. But I’ll submit it’s helpful to know what situations might be more stressing for your battery than others.

 

[jdw]

Unfortunately that blogpost predates the model 3. And Tesla changed a lot in the model 3. My information comes direct from the Tesla Model 3 service manual. Not someone's opinion.

Sorry, forgot I was in a Model 3 forum ... so I read Zoomit's link to a service manual excerpt on Reddit, and all of it makes sense and correlates with what is known about Model S batteries, except the last bolded line about leaving the car sit idle for hours/days.

Speaking for the S, the bleeder resistors are activated the same way, but once balancing is triggered the BMS then knows all the module voltages and how much to bleed off each one and can do that under normal operating conditions, with no need to leave the car sit.

I could see that bolded line making sense if the main point was that it can take many hours/days for the balancing to complete,

As to the activation of the balancing circuit, on the S it requires that the charging enters the constant voltage portion of the charging curve to trigger, so that may also be different between the two models.

 

[SilverString]

Last week I received a text message from Tesla Service in response to range loss. I was at 312-313 miles down from 335 over 23K miles and 11 months. Their response was that my battery cells were slightly out of balance due to my charging habits, and that had been corrected (how was not explained). They told me to charge to 90% every day using scheduled charging in the wee AM hours so as to allow the battery to rest before charging and to settle afterwords. Current range is 317. Until 2020.8.x my car was right in the middle of the pack for age and miles at approx. 325 on a 100% charge. After the update I lost 6 miles of range on the spot - immediately and it continued to head down to 312 when I scheduled a service call.

 

[GZDongles]

Not sure where you get that idea ... while it is true that balancing will not trigger until charging gets into the constant voltage curve, once triggered, balancing a) can take days and b) will continue whether sitting, driving or charging.

It's a complex and partisan issue, but discussed in depth in a number of places such as this blogpost on TMC. I'll go with wk057's opinion every time ;-)

I do charge to 95% to 100% every now and then to trigger balancing.

This brings up an interesting issue for the future when we all have 20% or greater battery degradation. Will the cells not balance when the battery has lost more than 15% capacity, or is the "85%" figure based on nominal pack capacity rather than original capacity? It seems like the BMS has to be technically capable of balancing the pack at <85% capacity.

Also my $0.02 with this discussion are that I don't care what the rated display range is if I'm not planning on using it. So I'd rather keep the SOC as low as needed day to day (probably 70% for me) even if that means the BMS will not have an accurate prediction of real range. As long as imbalanced cells don't do any long term damage, then who cares if the rated range is incorrect?

 

[jdw]

...

Also my $0.02 with this discussion are that I don't care what the rated display range is if I'm not planning on using it. So I'd rather keep the SOC as low as needed day to day (probably 70% for me) even if that means the BMS will not have an accurate prediction of real range. As long as imbalanced cells don't do any long term damage, then who cares if the rated range is incorrect?

The only potential issue with that, is that *if* you have significant unbalancing *and* you drive down below 5-10% or so, you run more risk of having a shut down. Most people don't have significant imbalance and most don't drive to extremes, so yeah, keeping the SOC lower is likely slightly better for battery health in the long term.