Using Lower Half Of Battery

[dusty22]

When I first got my M3 LR I would charge to 80%. After a while I realized that I was only doing local round trips averaging 12 to 15 miles a day with an occasional 50 mile trip.

I decided that I didn't need the whole battery for my purposes so I have been charging to 50% every day.

Is there any problem to exclusively using the lower half of the battery, say between 20 and 50 percent?

 

[Tam]

When I first got my M3 LR I would charge to 80%. After a while I realized that I was only doing local round trips averaging 12 to 15 miles a day with an occasional 50 mile trip.

I decided that I didn't need the whole battery for my purposes so I have been charging to 50% every day.

Is there any problem to exclusively using the lower half of the battery, say between 20 and 50 percent?

No problem for your battery health.

However, your battery gauge might be miscalculated.

For the BMS accuracy, Service Center wants you to set your charging at 90% for the traditional Lithium battery. For Lithium Ferrous, it's 100%. Again, those settings are for the benefit of the BMS accuracy and not about battery health.

 

[Regaj]

Your new charging regimen is much healthier for your pack than your old charging habit.

 

[3sr+buyer]

Using 20-50% is generally better for battery longevity compared to using 50-80%. NCA batteries like in the LR probably degrade less when under about 55%.

The only real issue is that the BMS may eventually get to estimating capacity and/or state of charge incorrectly. So an occasional (for NCA batteries) or weekly (for LFP batteries) charge to 100% may help resync the BMS.

 

[dusty22]

For the BMS accuracy, Service Center wants you to set your charging at 90% for the traditional Lithium battery. For Lithium Ferrous, it's 100%. Again, those settings are for the benefit of the BMS accuracy and not about battery health.

I was aware of the LFP Battery needing 100% now and then for BMS accuracy but have never heard of BMS maintenance of the other batteries. Thanks for the info. How often must one charge to 90% to maintain BMS accuracy?

 

[Tam]

I was aware of the LFP Battery needing 100% now and then for BMS accuracy but have never heard of BMS maintenance of the other batteries. Thanks for the info. How often must one charge to 90% to maintain BMS accuracy?

Nightly or as often as you can as some don't have a way to plug in at home.

 

[dusty22]

Nightly or as often as you can as some don't have a way to plug in at home.

I got my idea for a lower charge from this video but he doesn't talk about any BMS issues. Did you get the 90% recommendation from Tesla?

 

[Tam]

I got my idea for a lower charge from this video but he doesn't talk about any BMS issues. Did you get the 90% recommendation from Tesla?

No! But someone on youtube did!



Here's the receipt from the Service Center for someone else:

Service appointment for 12 month old Model 3 for range loss /invoice for out of warranty inspection?

If you don't mind, would you please post a picture of the receipt showing the charge level recommendation of 90%? Thanks! Here you go TAM.

teslamotorsclub.com

It reads:

"Concern: Customer states: 50 miles range loss. I have a gradual drop in range displayed when charging to 80%. I drove the model 3 to 5% then charged to 100% to see if that would help recalibrate the range being displayed At 100% charge my range displayed was 264 miles versus the 310-315 it normally shows.

Please tell the client NOT to discharge the car below 10% over the next few weeks. Issue caused by the clients charging habits. They consistently charge between 85% and 65% with rests near 60%. Please educate the client their charging habits as well or they will likely end up in the same situation again. Recommend charging to 90% every night. Irregular charging can cause a slight battery cell imbalanæ and may affect the rarnge estmation, although true range is not affected. Charging the vehicle every night will allow the battery cells to balance and improve range estimation."

 

[Regaj]

There's a very long thread on the forum here (How I Recovered Half of my Battery's Lost Capacity) which discusses the whole question of charging patterns and how they affect both real pack capacity and capacity as reported via the BMS. As you might expect, most of the sources for the information in that thread are anecdotal. The thread is certainly worth a read - there's quite a lot of interesting stuff in it. But the TL;DR version is that "calibrating" the BMS and other such contortions remain an unproven way to preserve pack health.

Certainly, a Tesla SC employee recommending that a customer charge their NCA-chemistry vehicle to 90% every night is the worst possible advice. And although I like Kim Java just fine, she has never struck me as much of an engineer. Deep dives into arcane technical topics is not the bailiwick of her YouTube channel.

There are many, many reputable research studies on the behavior of Lithium-ion batteries. For those who have an interest in such things, that's where I recommend they look.

 

[ay221]

I charge to around 55%. Try to charge it every couple of days at least. I do have the performance version. So only thing I'm missing out is acceleration, but I would burn out the tires quicker.

 

[GtiMart]

There are multiple conflicting "goals", which is why it's so difficult to get a proper recommendation. The thread you indicate @Regaj is indeed great for BMS calibration, which helps get good readings. It goes partly against recommendations on battery health. Battery health (keeping SOC low as much as possible) might cause range anxiety or make it problematic in case of an emergency where the car needs to be driven a long distance immediately.

By recommending to charge to 90%, Tesla would push aside many types of critics that say an EV isn't practical because of its low range and slow charging. They also favor reasonable BMS health. I believe that's also why they recommend 100% weekly for LFP batteries, even if that might not be best for the battery's health.

It's all about tradeoffs and conflicting priorities, like in almost anything in life.

 

[dusty22]

Very informative Tam, Thank You

 

[Tam]

...Certainly, a Tesla SC employee recommending...

When it is documented in a Service Center receipt, it's a documented policy not only to one owner at one location but others as well.

90% nightly is about BMS accuracy, not about battery health.

Owners don't charge at 90% and keep coming in complaining their battery is "degrading", it's losing miles on the battery gauge. So to solve the battery degradation anxiety, Tesla decided on that 90% practice.

If you want to set your battery at a low State of Charge for battery longevity, that's another practice, but that doesn't address the battery degradation anxiety.

 

[jjrandorin]

I was aware of the LFP Battery needing 100% now and then for BMS accuracy but have never heard of BMS maintenance of the other batteries. Thanks for the info. How often must one charge to 90% to maintain BMS accuracy?

I believe someone has already pointed you to the "how I recovered my lost capacity" thread. Keep in mind that ANY capacity that can be "recovered" is not actually lost in the first place, its simply BMS inaccuracies / drift.

From the many (many many many many many) posts / threads on this topic, in model 3s / Ys, people who charge to lower than 90% (because of various reasons) tend to experience more drift of "the number on the screen". At 90% the car does some sort of slow cell balancing that doesnt happen at lower levels of charge.

Note that the BMS drift in these cases is "the number on the screen", not actual capacity, because actual capacity loss isnt coming back.

So, TL ; DR your plan is better for battery health, how much better is debatable, and also possible (likely) to introduce some drift of the number on the screen that the car reports as range, to have it report less range than your car may actually have.

 

[Tam]

Very informative Tam, Thank You

Put it in another way.

You should not worry too much about Tesla batteries in general. It's great to know the principle, but even when you deviate from it, it's still very enduring.

Tesloop did the worst charging practice: 100% every time, and each time was not regular 120/240V but superchargers.

It degraded 6% at 194,000 miles.

Here's how a Tesla Model S holds up after 400,000 miles in 3 years

Tesla’s vehicles are becoming increasingly popular with taxi and shuttle services, which are pushing their vehicles a lot over short periods...

electrek.co

Thus, if you don't plan to run your car to almost 200,000 miles and risk a 6% degradation, the obsessive fear of doing something wrong for your battery health by following Tesla's instruction of 90% is unfounded.

 

[jjrandorin]

Put it in another way.

You should not worry too much about Tesla batteries in general. It's great to know the principle, but even when you deviate from it, it's still very enduring.

Tesloop did the worst charging practice: 100% every time, and each time was not regular 120/240V but superchargers.

It degraded 6% at 194,000 miles.

Here's how a Tesla Model S holds up after 400,000 miles in 3 years

Tesla’s vehicles are becoming increasingly popular with taxi and shuttle services, which are pushing their vehicles a lot over short periods...

electrek.co

Thus, if you don't plan to run your car to almost 200,000 miles and risk a 6% degradation, the obsessive fear of doing something wrong for your battery health by following Tesla's instruction of 90% is unfounded.

I have seen people mention tesloop before, but I dont feel that experience is relevant to model 3s. Those were model S with different batteries. With that being said, I agree with you in principle, but the tesloop example makes it sound like any model 3 with more than 6% degradation after a year or so is outside the norm, and there are enough reports of more degradation on model 3s / Ys than that, that I dont believe model S/X experience applies.

 

[dusty22]

Note that the BMS drift in these cases is "the number on the screen", not actual capacity, because actual capacity loss isnt coming back.

I understand. Would that mean you could drive more miles than normal past 0% since the battery has more charge than indicated?

Since I'm new at to EV's, I don't know if this means anything. I have been charging to 50% for a few months now. When the charging stops at 50%, the screen also displays 179 miles range which is exactly half the stated range of a M3 DM LR. Could that be accurate?

 

[Tam]

I understand. Would that mean you could drive more miles than normal past 0% since the battery has more charge than indicated?

I wouldn't put it in that way with low state of charge near zero.

Driving and then parking at a low state of charge is unpredictable.

That means if the Supercharger is 5 miles from the hotel and my gauge says there are still 10 miles left. Should I drive 5 miles to the Supercharger first or check in with the hotel and take a break first?

If you take a break first when your car has 10 miles left, by the time you go back to your car, it might say it has 0 miles or very few miles left and you won't make it to the Supercharger 5 miles away.

It's more prudent to charge first before you take a break when you are near zero.

However, when talking about you having 179 miles on your battery gauge and the BMS is drifting. It may mean you still have more, like a 190-mile capacity.

So when your BMS is correcting itself someday and as usual, you set it at 50% and expect 179 miles when you wake up, but this time it may say 51% and 190 miles! The old 50% was not really 50%, you were setting it at 51%, and you didn't know it until the BMS corrects itself!

 

[AlanSubie4Life]

Would that mean you could drive more miles than normal past 0% since the battery has more charge than indicated?

No, probably not.

. When the charging stops at 50%, the screen also displays 179 miles range which is exactly half the stated range of a M3 DM LR. Could that be accurate?

Yes.

A lot of the stuff on miscalibration has improved over the years so I would ignore any information more than one year old.

I charge my car routinely to 50-60%, and the extrapolated value is within a couple % of what I expect when I charge the vehicle to 100%. No apparent drift.

And when I drive the car and meter the energy, it proves that the BMS capacity estimate is within about 1%. So no issues there.

I just wouldn’t worry about any of this unless it seems abnormal. Charging to 50% is fine and good. Expect a couple % extrapolation error on the full range.

And expect capacity loss to occur, perhaps 10% in the next 3-4 years, or maybe a bit better if you are lucky.

 

[jjrandorin]

Would that mean you could drive more miles than normal past 0% since the battery has more charge than indicated?

You should never (ever) plan on driving "past zero" in any EV unless you are prepared to get your car towed either home or to the nearest charging station.