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Preheating vs. shallow discharge

yourrealdad

Member
Oct 15, 2019
5
3
Colorado
Hello,

New owner of a LR AWD M3 (did I abbreviate that correctly?).

We live in CO in the mountains so cold weather with temps falling down to -20F not out of the question. Car will be garaged, but still looking at temps in the garage to be below freezing in some cases.

I am a little confused on how to properly treat the batteries.

Do I preheat, which I don't really understand. Is this just turning on the car and not driving it for an hour? Is it just having it plugged in. I can't really find a solid concise instruction for what preheating is and how to preheat a M3.

It also doesn't make sense to me that preheating is turning on the motors to generate heat. Doesn't running the motors require the batteries to be discharging, thus defeating the purpose.

Additionally, Lithium in general doesn't like to be charged below 32F/0C, but also prefers to not discharge past -4F. You can do either of these beyond the range but with degradation and often permanent damage to the battery, so if it is -20F out how are Tesla's protecting the battery? Having the BMS shut it down doesn't seem like a safe way to handle things in a car.

If that is the case, then what about shallow discharge? This is my wife's car and she has a 80 mile total commute. So if we plug it in every night or very least in the morning then we are never getting that deep discharge and are constantly charging between 75%-90%.

Thanks for the feedback
 
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gecko10x

Member
Jan 22, 2018
265
165
WV
Preheat: The best way to preheat the battery is by charging. You can accomplish a preheated battery by timing the charge (or final 5-10% of the charge) to finish when you plan to leave. You can also sort of pre-heat the car by turning on the interior heat, but this is significantly less effective.

Shallow charging cycles are technically better for lithium batteries, as is keeping the state of charge closer to 50%. However, you have to square that with keeping the BMS happy (occasionally charging up to 90+% supposedly helps, as does discharging down to a lower SOC, like 20%), and having enough charge available to you for unplanned trips. Also, keep in mind that in the winter your range will suffer by at least 20%, and at the temps you referenced, I would think more like 40+% (BTW, preheating can help mitigate this).
 

doghousePVD

My grandfather’s car
Dec 3, 2018
648
597
New England, USA
The Stats app has a good charging/preheat program. Basically, schedule your charge so it is charging for at least an hour before you leave. So, charge your battery to 80% overnight, then restart the charging to go to 90% at 7am so the battery is ready to go at 8am. Also, turn on your cabin heat early, too.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,762
8,340
Boise, ID
I am a little confused on how to properly treat the batteries.
You don't need to treat the batteries; they will take care of themselves. It sounds like you are thinking that you have a job to protect the batteries from getting damaged from the cold or something. That's just not a thing--they will be fine if you do nothing.

The only thing that people's recommendations are for are just for how you feel driving the car. The part you mention about not being able to recharge when they are very cold is true, but the car knows this and will prevent charging until the battery can be warmed up. So that will be noticeable in the regenerative braking being very limited when it is cold, and you will have to use the real brake pads a bit more. So these recommendations from people about charging before you leave, etc. do warm the batteries up some and will make that regenerative braking more available from warming things up a bit.

But I just wanted to reassure you that you don't need to do anything to save your batteries.
 

nicholb

Member
May 2, 2018
185
313
Minnesota
There are two types of preheating.

1. Cabin preheating. Simply turn on climate control 30-60 minutes before you leave in the morning. The primary benefits of this are to use wall power to get the car up to comfort levels, and somewhat to warm the battery. Cabin heat is one of the larger causes of winter range reduction so if you can do it from wall power you won't have to use up your battery charge to stay comfy.

2. Timing your charging. Either with a 3rd party app or manually, finish the last 10% of your charge in the morning before leaving. This will cause the battery to be warmed and give you more winter range and high levels of regen.

Personally I just do the cabin preheat as I have plenty of range for my daily driving.
 
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jdw

Supporting Member
Supporting Member
Jun 1, 2015
702
1,390
Vancouver
You can preheat the car by turning on the climate - it will warm the cabin and if it is cold enough, also the battery. The Model 3 uses the motors and inverters to generate heat which is circulated through the battery. Draws about 6kW to operate the battery heater and about the same for the cabin heater at full blast.

Lithium batteries do not like being charged when they are cold (lithium plating and dendrites), but discharging when cold is not an issue. Tesla protects the battery by limiting charge rates and reducing regen when the battery is cold. If your garage is not heated, you can help out by charging when you get home at night as the battery will still be warm from driving. If you are plugged in, you can still preheat in the morning to warm both the cabin and the battery. If you are not plugged in, don't bother preheating, just get in and drive.

Finally, lithium batteries prefer many shallow discharges over fewer deeper discharges. Charging from 75-90% is not an issue, in fact it will help keep your estimated range accurate. Every now and then you will likely drive down below 75% or require a 100% charge anyway - doing this occasionally seems to be enough to keep the range estimate in line. Ideally, the car is happiest no lower than 20% and not above 90% during operation, with long term storage around 50%.

I have five years of charging from 75-80% to 90% daily with zero degradation. The only time my range has temporarily dropped has been either missing charging for a day or two or charging below 90% . I do usually time charging to finish just before I leave, but I have a heated garage.
 
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yourrealdad

Member
Oct 15, 2019
5
3
Colorado
How is charging warming the battery before it is used and how is the battery protected from discharging at a lower temp? Lets say I park outside on a -20F night and then drive my car away then the batteries have to be discharging when they are -20F? If I plugged the Tesla into a super charger outside then they are taking charge at -20F which is even worse. I just don't understand how the batteries can be used to run a motor to heat up the batteries to protect the batteries. Seems a little chicken/egg ish.

Also according to Tesla cabin heating doesn't precondition the battery.

Interesting, for some reason I had heard that Lithium like deep discharges. I will try to keep it around 50-90%

Wasn't there a version initially that was LR but not AWD? I thought there was a LR single motor version in the beginning?

Yep M3 makes me think of BMW
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,762
8,340
Boise, ID
Pretty decent questions here, but they all have good answers.
How is charging warming the battery before it is used and how is the battery protected from discharging at a lower temp? Lets say I park outside on a -20F night and then drive my car away then the batteries have to be discharging when they are -20F?
Discharging when very cold is not nearly the problem as charging when very cold for li-ion batteries. You will possibly see a slight power limiting when first starting to drive with a very cold battery like that, but not very much. You can drive and discharge a very cold battery, and it is OK.

If I plugged the Tesla into a super charger outside then they are taking charge at -20F which is even worse.
I see you haven't done this yet. You are right that it would be incredibly damaging, which is why the car's battery management system knows not to do that. You will plug in, and...nothing will happen for a while. It will be drawing some single digit numbers of kW power for a while just running heating, with NO charging happening yet until it can get the battery temperature up to about freezing or above to begin very slowly charging. This is why it is a practical consideration if you are on a multi-day trip when it is very cold, relying on just Superchargers instead of overnight charging, to stop by the Supercharger when you arrive in the overnight city to mostly fill up before going to your hotel. Otherwise, if you let the car sit overnight, getting down to 0 degrees and then go to the Supercharger in the morning, you plug in and can be waiting 20, 30+ minutes for it to warm the battery to get to start some decent charging.

I just don't understand how the batteries can be used to run a motor to heat up the batteries to protect the batteries. Seems a little chicken/egg ish.
Again, because of discharging when cold not being a problem, and the battery must get up to a non-freezingish level to be able to charge at all and to an even warmer level to get decent speed of charging.

Also according to Tesla cabin heating doesn't precondition the battery.
It's possible this could be a Model S/X versus 3 difference. Read the descriptions of it in the manual. It does or doesn't depending on temperature. Most of the time it doesn't, but it says that below freezing, it can also do the battery heating when you turn on cabin heat. This will be indicated in the phone mobile app with a snowflake icon inside the battery meter display.

[EDIT] I just conveniently found a Model S thread where someone posted a snapshot of their mobile app asking "What is this icon?" and it's the icon showing battery warming being on from cabin preheating when it is extra cold. So that is what the icon looks like in the app if you ever see it with your Model 3.
Battery warming icon?

Interesting, for some reason I had heard that Lithium like deep discharges. I will try to keep it around 50-90%
No, that is some leftover tribal knowledge about ni-cad batteries that would develop "memory" effect. For li-ion ones, living in mid-range is always healthiest, but it does usually cause the meter display to lose calibration from using it in a small band like that, so it's just for people's own warm fuzzy feelings that you might exercise it high and low to regain some of that reading accuracy.

Wasn't there a version initially that was LR but not AWD? I thought there was a LR single motor version in the beginning?
Yes, long range single motor definitely was sold for a while, but I think they've dropped it for now to simplify builds/options. I would bet that it will probably be brought back again sometime in the next year or two when they have the capacity to deal with more versions again.
 
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pdx_m3s

Active Member
May 18, 2019
1,369
1,242
Portland, OR
Try to time your charging so it finishes close to around the time that you leave. This will make the biggest difference.

Also, preheat the cabin much hotter than you need while plugged in and then turn down the heat when you actually leave. This will help with energy efficiency while driving.

Shallow charges are actually better for Li-ion batteries, so plug in every night and set you charge limit accordingly.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
6,762
8,340
Boise, ID
Also, preheat the cabin much hotter than you need while plugged in and then turn down the heat when you actually leave. This will help with energy efficiency while driving.
o_O Uh...why would you want to waste a bunch of energy getting the car extra hot and losing it through the windows while you are not even there to supposedly gain "energy efficiency" when you drive? If you care about efficiency, you wouldn't waste excess energy first before you leave. That makes no sense. If you just let it heat as you drive, it only uses as much as it needs. Obviously there are other valid reasons for preheating on shore power, like just for comfort or if you need to squeeze every bit of range on a drive, but "efficiency" sure isn't it.
 

pdx_m3s

Active Member
May 18, 2019
1,369
1,242
Portland, OR
o_O Uh...why would you want to waste a bunch of energy getting the car extra hot and losing it through the windows while you are not even there to supposedly gain "energy efficiency" when you drive? If you care about efficiency, you wouldn't waste excess energy first before you leave. That makes no sense. If you just let it heat as you drive, it only uses as much as it needs. Obviously there are other valid reasons for preheating on shore power, like just for comfort or if you need to squeeze every bit of range on a drive, but "efficiency" sure isn't it.

By energy efficiency, I meant driving energy efficiency. While the car is pre-heating on shore-power, it's slowly warming up all the
materials in the cabin as well, which is less for the car to have to do while only on battery power. It will increase driving range, if that's what one is after.

You are correct that it will use more overall electricity. As with any science-related question, it's always important to define the system. I should have been more clear.
 

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