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How often should we charge to 100%?

Ames

Member
May 27, 2013
659
380
Abu Dhabi, UAE
All your cells get charged together, and each one to 90%.

If you never charge to 100% there is no harm. If you do charge to 100% try to drive soon after, i.e. don't leave the car fully charged for a long time like overnight.

Constantly supercharging is not ideal for your battery because it tries to put in as may kW as it can take, which produces a lot of heat, which ultimately wears down the battery...so ideally your normal charging is low power and supercharging for road trips.
 
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boaterva

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Apr 2, 2016
7,594
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Northern Virginia, USA
Another point is that charging to 100 is hard because it slows down the higher you get. I try to charge to 100 for road trips (usually on my HPWC) but only start it a few hours in advance when the car’s st its normal 80 so we only end up at 90 or 95 usually. Supercharging takes a while to get there too.

As was said, there’s no problem going to 100 if you are going to use it ‘soon’ as in the next few hours. It’s good once in a while to ‘fill er up’ to recalibrate things but once every few months should be enough if you haven’t done it for a road trip or otherwise.

I keep my 100 kWh pack at 80 normally, plugged in all the time. You have a slightly different use case not having L2 at home.
 
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Testwa

Member
Dec 23, 2016
51
13
Germany
I think once in a while balancing of the cells should be done. And this is done only when being close to 100% SoC.
The problem that might happen without balanced cells is that over time each cell has a different voltage. And when being at an low SoC (close to 0%) some cells might be still above the minimum voltage level while others are already below the minimum voltage level. And the latter one can cause more severe battery degradation. To avoid this unbalanced voltage at low SoC either always avoid low SoC or do balancing once in a while.
 
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AmpedRealtor

Well-Known Member
Jun 30, 2013
6,414
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Phoenix, AZ
I've never needed to charge to 100% yet. I exclusively Supercharge to 90% as it's nearby and my rental townhouse doesn't have L2 charging.

Does only charging to 90% mean the same 10% of cells never get charged? How often should you go to 100% even if you don't need to?
Simple rule of thumb: Whenever you need to.
 

henderrj

Active Member
Jun 16, 2014
1,064
947
Graham, WA, United States
In at least one study, a search should ferret it out, it was shown that supercharging actually is better for the battery. The theory is that the battery is hot for less time. I know that we've supercharged quite a bit, and to 100% at least 50 times. Only a few times that I left it overnight, and we still have 259 rated miles when we charged to 100% the other day (accidentally). We're just about to pass 90k miles total, still the original E battery. The point being, don't sweat it! You have an eight year unlimited mile warranty anyway. Enjoy the car!
 

FlyF4

Son of a MX
Mar 21, 2017
851
675
moved to San Diego
In at least one study, a search should ferret it out, it was shown that supercharging actually is better for the battery. The theory is that the battery is hot for less time. I know that we've supercharged quite a bit, and to 100% at least 50 times. Only a few times that I left it overnight, and we still have 259 rated miles when we charged to 100% the other day (accidentally). We're just about to pass 90k miles total, still the original E battery. The point being, don't sweat it! You have an eight year unlimited mile warranty anyway. Enjoy the car!
I'm not so sure I buy the theory from that study. While I agree that heat is an enemy of batteries, when on a home charger or destination charger, the battery pack barely gets warm at all. And let's don't forget the cooling that occurs if the algorithms determine that coolant needs to be pumped through the pack. I have never seen that happen on a home / destination charger unless it is super hot outside.
 

David99

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Jan 31, 2014
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Brea, Orange County
Does only charging to 90% mean the same 10% of cells never get charged? How often should you go to 100% even if you don't need to?

No. All cells are equally used all the time. If the whole battery pack is charged to 90% all battery cells are at 90%. So all cells are getting used equally and there is nothing you need to worry about. It is a good idea to charge to 100% here and there (maybe every other month) to help the battery management software be more accurate calculating the remaining range.
 
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Hugh Mannity

Mediocre Member
Jul 31, 2014
1,349
831
Calgary, AB
I think once in a while balancing of the cells should be done. And this is done only when being close to 100% SoC.
The problem that might happen without balanced cells is that over time each cell has a different voltage. And when being at an low SoC (close to 0%) some cells might be still above the minimum voltage level while others are already below the minimum voltage level. And the latter one can cause more severe battery degradation. To avoid this unbalanced voltage at low SoC either always avoid low SoC or do balancing once in a while.

Don’t believe this is true. Cell balancing happens elsewhere in the % range of the pack when you are plugged into shore power. The BMS system is pretty smart and it operates routinely to ensure the health of the pack. Having said that I charge to 100% every so often to “exercise” the pack even more.
 
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sorka

Well-Known Member
Feb 28, 2015
8,608
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Merced, CA
I'm not so sure I buy the theory from that study. While I agree that heat is an enemy of batteries, when on a home charger or destination charger, the battery pack barely gets warm at all. And let's don't forget the cooling that occurs if the algorithms determine that coolant needs to be pumped through the pack. I have never seen that happen on a home / destination charger unless it is super hot outside.

My battery temps run the same whether I'm charging at 80 amps or on a supercharger (about 105 to 108) *if* the ambient temperature is in the mid 70s or higher. The difference is that while supercharging the cooling system is working much harder to keep the temperature in that range vs when it's charging from an HWPC.

So in many cases, supercharging will result in less heat exposure over time. But there are also cases where this is not true like if it's very cold outside.
 
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Testwa

Member
Dec 23, 2016
51
13
Germany
I've seen some videos that show most cell balancing already starts to occur at around 92% SOC.
Balancing means that cells that are fully charged are not charged any longer and cells that are not fully charged yet are still being charged to bring all cells to the same level, hence the name balancing. So starting balancing at 92% would probably mean:
  • either that some cells are already at 100% while others are maybe still around 84% ... so in average 92%. I think that would mean heavily unbalanced batteries. Seems unlikely to me for what I have read so far about the batteries in Teslas.
  • or that already at 92% the cells with higher voltage are not charged any longer and are waiting for the cells with lower voltage to keep up. That seems not wise to stop charging some cells before they are full.
So balancing should start only when the first cells are fully charged and other cells are not fully charged yet.
With LiPo batteries for RC cars you can easily monitor the voltage of the different cells. After a full charge and then after driving the RC car you can see the voltage of the empty cells differs slightly. To bring them to the same 100% level, fully charged cells may not be charged any longer but balancing has to kick in to continue charging the weaker cells.
 
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David99

Active Member
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Jan 31, 2014
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Brea, Orange County
Balancing means that cells that are fully charged are not charged any longer and cells that are not fully charged yet are still being charged to bring all cells to the same level, hence the name balancing.

Balancing on the Model S/X battery works different. At some point the BMS measures and determines how much energy the difference is. It uses resistors to bleep off the higher cell groups to match the lowest ones. It does that by applying the resistors a certain amount of time. This happens completely independent of what the car does. It can be parked, it can be charging or driving. It doesn't matter. Once the difference is determined it will runs it's resistors. This way balancing is independent of charging which is an advantage.

We don't know exactly what and when the BMS is measuring to determine the difference. Jason Hughes, who has taken Tesla batteries apart early on has found balancing seems to be triggered at aprox 92-93%.If that means they are only measured at this SoC is unclear. There might be other things the BMS does to determine differences. I have monitored the cell voltages for over two years on my battery. The differences are bigger at lower state of charge, so it is easier to see them at a lower state of charge.

Either way, if you look how the battery is designed, the cell groups cannot be charged independently so the only way balancing works is through the resistors bleeding off the higher cell groups.
 

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