# Simple(r) Battery Rebalancing?



## JasonF

I normally charge my almost two year old LR RWD Model 3 at 10:30 pm, set to charge to 90%. It used to charge up to 285 mi range, which is what I would start my day with. That slowly began to creep down over the next few weeks so I would end up with anywhere between 279 and 283 mi of range.

So I decided ahead of time to try and rebalance the battery a little bit at a time, because I don't really like to drain it all the way to zero (I didn't like to do that with my former gasloline car, either). So I decided to skip exactly one day (Sun night) charging. Tuesday morning I woke up to see 287 miles of range!

I guess that means the battery just needs a _little_ more room to do the cell rebalancing. As I get closer to the weekend, I'm going to attempt not charging for two days, and see if that extra breathing room will let the battery rebalance some more, or if it has no effect at all. And I'll also keep an eye on it and see if this is a fluke, and it quickly creeps back down to 279.

By the way, I got the inspiration for trying that from my laptop. If it has issues with quickly dropping charge level when unplugged, I usually run it down a little farther than I usually do, but not all the way, and then let it fully recharge.


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## Ed Woodrick

Remember that software versions WILL change the number, so don't get too worried about it.
I don't believe that there is ever a need to take it low, that's a holdover from NiCad days.
Just take it to 100% and leave it sitting there for a day or so. It's not going to hurt the battery. Preferably do it when you are going to take a trip and have a need to.
Problem with many laptops is that the charging profile is that they charge to 100% and stay there, often for months and years. Many manufacturers are now implementing profiles that allow you to reduce the max charge. You may not get to specify the %, mine is called something like "Plugged in mostly"

But there really is no need to worry about what it charges to, just enjoy the car.


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## iChris93

Ed Woodrick said:


> Just take it to 100% and leave it sitting there for a day or so.


My understanding is different than yours and I would suggest minimizing the amount of time left at 100% to as little as possible.


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## MelindaV

JasonF said:


> I normally charge my almost two year old LR RWD Model 3 at 10:30 pm, set to charge to 90%. It used to charge up to 285 mi range, which is what I would start my day with. That slowly began to creep down over the next few weeks so I would end up with anywhere between 279 and 283 mi of range.
> 
> So I decided ahead of time to try and rebalance the battery a little bit at a time, because I don't really like to drain it all the way to zero (I didn't like to do that with my former gasloline car, either). So I decided to skip exactly one day (Sun night) charging. Tuesday morning I woke up to see 287 miles of range!
> 
> I guess that means the battery just needs a _little_ more room to do the cell rebalancing. As I get closer to the weekend, I'm going to attempt not charging for two days, and see if that extra breathing room will let the battery rebalance some more, or if it has no effect at all. And I'll also keep an eye on it and see if this is a fluke, and it quickly creeps back down to 279.
> 
> By the way, I got the inspiration for trying that from my laptop. If it has issues with quickly dropping charge level when unplugged, I usually run it down a little farther than I usually do, but not all the way, and then let it fully recharge.


since the end of January I've been charging to 90% about 2x a week (when it gets down to 20%) a total of 10 times. in that amount of time, the total estimated range has gone up less than 1 mile. so don't think an extra down day without charging makes a difference and presume your change was a fluke.


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## JasonF

MelindaV said:


> since the end of January I've been charging to 90% about 2x a week (when it gets down to 20%) a total of 10 times. in that amount of time, the total estimated range has gone up less than 1 mile. so don't think an extra down day without charging makes a difference and presume your change was a fluke.


I don't think it was so much "skipping a day" as I don't normally drive far day-to-day, so maybe the battery needed a lower state of charge than it normally gets to in order to re-balance. What I'm generally getting at is maybe it doesn't take draining the battery all the way down to zero and then full charging it to do that (though maybe that might do it quicker).

But I also have exactly _one_ data point. I won't know if this works reliably until tomorrow - if it's back to 279 to 281 or so, that means it had no effect. It also means I don't yet know if it's repeatable.


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## JWardell

We know from Tesla's own documentation that the battery triggers balancing once over a certain voltage around 90%. Charging to 92% should be enough.
The actual balancing or recalibration won't necessarily occur there. Once it is charged above 90 and can sit long enough to sleep, then it may take a long drive or a reduction below 50% before it actually recalibrates its capacity.

Last week I positively triggered a rebalance and boost in range as verified both in CAN data and on Teslafi, after charging to 92%, an hour later I had a long drive. Then while the car was parked at 46% and only Sentry mode running, starting after 15 minutes the range started going UP as logged by Teslafi while it sat for a few hours. I later confirmed the CAN showed a higher total capacity afterwards (only about 0.5kWh in this case). I just happened to be very closely looking at various numbers and documenting things throughout that day as I'm preparing a deep dive video into the battery.


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## JasonF

JWardell said:


> We know from Tesla's own documentation that the battery triggers balancing once over a certain voltage around 90%. Charging to 92% should be enough.


That explains a lot, and some good news on this topic: After skipping one day of charging, the car decided to charge to 91.5% all by itself, without me moving the charge limit from 90%. That's when I had a sudden large increase. I guess the battery management knew it needed some rebalancing?

Today it settled back to 90%, only gaining 2 miles of range out of the attempted recalibration (which doesn't sound great, except that the original goal was to get back the 2 miles that dropped out of daily charging last week).

Because updates kept shifting the rated range at 90%, it's really hard to tell just how much is that and how much is actual battery degradation. When the car was new, 90% was 279 miles. After one update, 90% was 292 miles, but then another update knocked it back down to 288 or so. Where it's harder to tell if it's degradation or updates is when it crept down to 285, settled there for a while, then ended up around 282/283.

When it suddenly dropped to 279 again once was when I decided to try a rebalancing experiment. This morning it's at 282. Because I do timed off-peak charging starting at 10:30 pm, it's likely it went higher at the end of the charging session, and dropped a little overnight.


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## Ed Woodrick

iChris93 said:


> My understanding is different than yours and I would suggest minimizing the amount of time left at 100% to as little as possible.


Look at the studies around keeping batteries at 100%. Last I looked, they are suggesting that keeping a battery continuously at 100% for a year degrades that batter a FEW percent.
Indeed, my personal experience indicates similar and over 3 years, some battery swelling starts to occur. That's keeping batteries at 100% essentially 100% of the time.

People have taken that knowledge and extrapolated it to keeping it at 100% for 10 minutes is a bad thing, that's very far from reality.
BMS doesn't start kicking in until about 92%, but it can't bring the batteries to full charge unless it is at 100%. And since the amount of current that a battery will accept is very small when near full, it can take a few days to get that last little bit out of it.

But again, don't worry about it. Take a long trip every few months, charge to 100% when you do. And no don't wait until the last minute to charge to 100%.

Tesla didn't design the battery for you to have to worry about. Last I heard, the Model 3 was trending for about 300,000 miles usable lifetime. That means that the battery is probably going to far outlive the amount of time that you are driving the car.


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## garsh

Ed Woodrick said:


> Look at the studies around keeping batteries at 100%. Last I looked, they are suggesting that keeping a battery continuously at 100% for a year degrades that batter a FEW percent.


Counterpoint:

*"the amount of damage was the same whether the battery was kept at 4.3v for 28, 53 or 100 mins so it didn't seem that longer time at 4.3v was worse but all 3 times were worse than just charging to 4.3v and immediately starting a 1C discharge cycle."*



Brokedoc said:


> The holy grail of Li-Ion battery life research dates back to an article by Choi, et al published in 2002.
> 
> Choi, S. S., & Lim, H. S. (2002). Factors that affect cycle-life and possible degradation mechanisms of a Li-ion cell based on LiCoO2. Journal of Power Sources, 111(1), 130-136. doi:10.1016/s0378-7753(02)00305-1
> 
> The specific chart pertaining to the lifespan damage caused when charging to 100% (4.3v) shows that the majority of damage occurs not so much when briefly charging to 4.3v but instead occurs when charged to 4.3v and held at that state.
> 
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> 
> Interestingly, the amount of damage was the same whether the battery was kept at 4.3v for 28, 53 or 100 mins so it didn't seem that longer time at 4.3v was worse but all 3 times were worse than just charging to 4.3v and immediately starting a 1C discharge cycle.
> 
> The Methodology page from the Accubattery app that I use on my Android phone is EXTREMELY informative and highly recommended for anyone wanterting to learn about maximizing Li-Ion battery lifespan. https://accubattery.zendesk.com/hc/...ing-research-and-methodology?mobile_site=true
> 
> There was also data from Choi 2002 that showed rapid charge of rates greater than 1C-2C resulted in lifespan degradation. Even using a current generation Tesla supercharger is not at 1C charging rate (0-100% in 60 mins) Future generation SC may be faster than 1C but not yet...


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## JWardell

garsh said:


> Counterpoint:
> 
> *"the amount of damage was the same whether the battery was kept at 4.3v for 28, 53 or 100 mins so it didn't seem that longer time at 4.3v was worse but all 3 times were worse than just charging to 4.3v and immediately starting a 1C discharge cycle."*


What the heck happened to brokedoc? Can't even @ him anymore...

I will also point out that the BMS also adjusts for average temperature over what may be weeks. For many of us, you really can't properly gauge battery range and degradation till we are in the summer again.


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## Ed Woodrick

garsh said:


> Counterpoint:
> 
> *"the amount of damage was the same whether the battery was kept at 4.3v for 28, 53 or 100 mins so it didn't seem that longer time at 4.3v was worse but all 3 times were worse than just charging to 4.3v and immediately starting a 1C discharge cycle."*


And what voltage is Tesla charging to vs max voltage? There really are SOO MANY gaps in this statement. Let alone it was 20 years ago when the battery chemistries were quite different.
How much damage was there? Was there a BMS in front of the cell? (Pretty sure the answer is no)

Even Tesla battery chemistries have change a lot in 7 years.


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## MelindaV

JasonF said:


> Because updates kept shifting the rated range at 90%, it's really hard to tell just how much is that and how much is actual battery degradation.


instead of looking at the range at a specific charge percentage level, it is more telling to look at the kWh added to the battery during a charge over a specific charge percentage...
IE, charge from 20-90% for a 70% recharge. how many kWh were added? if 50kWh were added for that 70% capacity, the total 100% capacity would equate to 71.428 kWh (math is 50/.7), or about a 4 1/2kWh decrease from a new LR Model 3 battery, or about 6% of a capacity loss.
the car's on-board display will not show the full kWh added (but rounded to the nearest whole number) and what actually went to the battery vs heat/cooling/etc, so you really need to get the kWh number added directly to the battery from the API (or via 3rd party sources using the API like Teslafi).


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## JasonF

MelindaV said:


> so you really need to get the kWh number added directly to the battery from the API (or via 3rd party sources using the API like Teslafi).


I'll leave the numbers to better qualified people. If I start doing that, with my lacking math skills, I'm definitely going to make a mess of it.  I'll stick to more plainly obvious results instead.

BTW, I tried a second balancing round, and though that time it didn't have a sudden charge limit increase, but it is (for now) consistently charging to a rated 283 miles. I guess that could mean it's as balanced as it can get right now.


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## Ed Woodrick

MelindaV said:


> instead of looking at the range at a specific charge percentage level, it is more telling to look at the kWh added to the battery during a charge over a specific charge percentage...
> IE, charge from 20-90% for a 70% recharge. how many kWh were added? if 50kWh were added for that 70% capacity, the total 100% capacity would equate to 71.428 kWh (math is 50/.7), or about a 4 1/2kWh decrease from a new LR Model 3 battery, or about 6% of a capacity loss.
> the car's on-board display will not show the full kWh added (but rounded to the nearest whole number) and what actually went to the battery vs heat/cooling/etc, so you really need to get the kWh number added directly to the battery from the API (or via 3rd party sources using the API like Teslafi).


OMG! Did you worry about the ounces of gas that you used?

This is just range anxiety!!! Get over it!!!

Most all of the work has already been done by the engineers, not much that end users can really do. These batteries are trending for 300,000 miles, isn't that enough?


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## MelindaV

Ed Woodrick said:


> OMG! Did you worry about the ounces of gas that you used?
> 
> This is just range anxiety!!! Get over it!!!
> 
> Most all of the work has already been done by the engineers, not much that end users can really do. These batteries are trending for 300,000 miles, isn't that enough?


it is not range anxiety and if you don't care if your car is losing more capacity than it should, fine. but others do care and you saying to get over it is BS. your example of gas used (efficiency) is not the same as capacity.


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## Ed Woodrick

MelindaV said:


> it is not range anxiety and if you don't care if your car is losing more capacity than it should, fine. but others do care and you saying to get over it is BS. your example of gas used (efficiency) is not the same as capacity.


What are you anxious about the life of the battery? 
How many cars have you seen losing more miles than they should? Except for obviously bad batteries that get replaced?
Has anyone demonstrated with the Model 3 battery a KNOWN GOOD or BAD method of maintaining the battery? Known good means one that has shown proven results of a change in battery life?

So, without a known method of treating a battery good or bad, what does worrying about it really do?

It's plain and simple range anxiety, not miles per charge, but miles per battery lifetime.

Just tell me a PROVEN way that I can make my battery last longer.


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## FRC

Hey, Ed, why not let Melinda(and others) tend to their cars and batteries as they see fit. They don't have to see it your way or act your way. And they aren't trying to tell you how to act with your car. Please, lay off.


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## JasonF

Ed Woodrick said:


> What are you anxious about the life of the battery?


That's not the point. I know the characteristics of lithium based batteries, and that they tend to get out of balance, which causes a small amount of their capacity to become unavailable. I also know that _small _lithium based batteries tend to "reset" when you drastically change your charging behavior. So I'm exploring just how small of a change to charging behavior it takes to nudge some of the unavailable capacity in the Tesla battery back into use. As with all experiments, "failure is always an option". If it ultimately makes no difference, it's no problem.

I don't _need _ the extra capacity - I'm just playing with the battery characteristics. Same way anyone who goes on a long drive in an EV doesn't _need_ to hypermile the whole way, but it's sort of a game.


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## Dr. J

JWardell said:


> We know from Tesla's own documentation that the battery triggers balancing once over a certain voltage around 90%. Charging to 92% should be enough.
> The actual balancing or recalibration won't necessarily occur there. Once it is charged above 90 and can sit long enough to sleep, then it may take a long drive or a reduction below 50% before it actually recalibrates its capacity.
> 
> Last week I positively triggered a rebalance and boost in range as verified both in CAN data and on Teslafi, after charging to 92%, an hour later I had a long drive. Then while the car was parked at 46% and only Sentry mode running, starting after 15 minutes the range started going UP as logged by Teslafi while it sat for a few hours. I later confirmed the CAN showed a higher total capacity afterwards (only about 0.5kWh in this case). I just happened to be very closely looking at various numbers and documenting things throughout that day as I'm preparing a deep dive video into the battery.


@JWardell, do you have a sense of whether the balanced battery will actually have more energy and go farther than the battery in an imbalanced state? Let's saying I'm taking a road trip requiring all the battery has (Amarillo to Trinidad, e.g.); would it help to balance the battery prior to the trip, or just charge to 99%-100% when I get to Amarillo and not worry about it?


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## tencate

JWardell said:


> I will also point out that the BMS also adjusts for average temperature over what may be weeks. For many of us, you really can't properly gauge battery range and degradation till we are in the summer again.


I think I'm seeing this now. It's been pretty nasty cold this winter but lately we've had a few weeks of quite warm weather. I'm clearly seeing better range numbers now than just a few weeks ago. Nothing quantitative or scientific but enough of a change that I've had to check a couple of times to be SURE I was only charging to 80% instead of 90%. Near as I can tell, I'm back to around seeing 315+ miles of range again instead of 300. This with a car with nearly 60k miles. Maybe I'm lucky?


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## JWardell

Dr. J said:


> @JWardell, do you have a sense of whether the balanced battery will actually have more energy and go farther than the battery in an imbalanced state? Let's saying I'm taking a road trip requiring all the battery has (Amarillo to Trinidad, e.g.); would it help to balance the battery prior to the trip, or just charge to 99%-100% when I get to Amarillo and not worry about it?


A balanced battery will let you charge higher, and that will let you drive further, yes. It's all about worst-case packs and cells, so your charge can only go as high as the highest voltage cell hitting the limit, and your drive can only go down to the lowest cell hitting the lower limit. The closer they are to each other, the less drastic the difference is.


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## Dr. J

JWardell said:


> A balanced battery will let you charge higher, and that will let you drive further, yes. It's all about worst-case packs and cells, so your charge can only go as high as the highest voltage cell hitting the limit, and your drive can only go down to the lowest cell hitting the lower limit. The closer they are to each other, the less drastic the difference is.


Thanks!


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