Absolutely Best, Proven Method to Warm a Cold Battery

[dansev]

I've been wrestling with this question every winter since I got my M3 in 2019. Is it better to warm the battery by charging--timing my charge so that it finishes just before I leave? Or is it better to turn on the heat before I go? And for how long? And at what temp? Lately I have been doing a combination of all this stuff. I have my charging start at 4:30 am, but my departing/commuting time varies, so it could be a couple hours before I drive off. Not ideal? No big deal? And then I set the heat to 60 degrees for 20 minutes or so, basically to just start warming the battery, because there doesn't seem to be any other method of officially sending heat to the battery, (if charging is done.) And then about 10 minutes before I get in the car, I increase to 74 degrees just so the cabin is toasty. Then I reduce to 68. But even when I time all of this perfectly, with a long (~50%) charge, I still have many dots in the region indicator. I guess that's unavoidable? Sometimes I even increase the battery charge target a bit for the last 20 or so minutes before I leave just to heat it even more. Problem with that is that I can forget and overcharge the next day. None of this is ideal!!! Surely Tesla could come up with a less complicated solution. And yes, I have tried the Departure Precondition setting, but have been late to work because the battery wasn't even close to the set point when I needed to leave! Been hesitant to use it since then.

Please, experts, weigh in? How should I prepare my car given that I don't have a set departure time every day?

 

[jjrandorin]

You shouldnt worry about it at all unless you are driving your entire battery range out every day. Are you? If so, then yes you can try to micro manage this. If not, then there is no reason to worry about heating the battery before driving, especially now that you can have brake blended regen if you want.

You are not going to hurt the car in any way, shape or form by driving it with a cold battery. Heat the cabin for your comfort before you go, dont worry about heating the battery unless the next stop you are making is a supercharger.

To answer the question of "absolute best proven way to heat the battery in a model 3" its "use the navigation and point it to a supercharger that is close to you".

 

[stopcrazypp]

Are you charging the battery to higher SOCs? That will also limit regen. Also, AFAIK, setting heat to the cabin does not necessarily heat the battery very much, the system is able to work relatively independently. As mentioned, the only reliable way to actually heat the battery is pointing the car to a supercharger station.

 

[dansev]

Fascinating. But technically the loss of regen is wasting energy, no? I generally charge to 80/85% in the winter on days where I’ll drive a lot. Rarely past 90%. That doesn’t limit regen, does it?

So by preheating at home, I waste just as much energy as just driving off with limited regen? This is quite liberating information!

And, no, I rarely drive the whole battery. Some days I get home with 20%, especially in the winter. But it’s not too common. Ironically tomorrow I will be going on a long drive and I don’t want to charge until I get there. So before i leave I should set the nav to a supercharger nearby while still plugged in? For how long?

 

[stopcrazypp]

Fascinating. But technically the loss of regen is wasting energy, no?

If you do not apply much friction braking, loss of regen does not waste energy. In fact hypermilers get better mileage by coasting. Regen is not 100% efficient, so if you do a good job of coasting, actually you can be more efficient. However, if you apply the setting where it blends friction brakes to make up for loss of regen, that is a different case.

I generally charge to 80/85% in the winter on days where I’ll drive a lot. Rarely past 90%. That doesn’t limit regen, does it?

In my experience even here in California Bay Area (where weather doesn't get that cold), I still get the limited deceleration warning when going down a steep hill rapidly at those SOCs. When I charge below 70% that seems to be the way to ensure I don't get the message. I have a SR+ however, so YMMV depending on which version you have.

So by preheating at home, I waste just as much energy as just driving off with limited regen? This is quite liberating information!

As a function of total energy (taken out of the electrical supply from your home), pretty much yes. However, if you are short for range, preheating at home gives you extra stored energy (in the form of stored heat in cabin and possibly battery), so you will see more range vs driving off cold.

And, no, I rarely drive the whole battery. Some days I get home with 20%, especially in the winter. But it’s not too common. Ironically tomorrow I will be going on a long drive and I don’t want to charge until I get there. So before i leave I should set the nav to a supercharger nearby while still plugged in? For how long?

Setting nav to a supercharger enables battery conditioning, but from the points above, it is largely unnecessary unless you were actually intending to supercharge at your location (primary benefit is increasing charging speeds). How long the battery takes to warm up to optimal conditions would depend on your actual conditions, I don't think anyone can give a solid answer. Even determining it yourself, you probably need to buy a OBD tool to get the actual battery temp measurements to determine this.

 

[Watts_Up]

Please, experts, weigh in? How should I prepare my car given that I don't have a set departure time every day?

First thing would be to use the phone App 'Scan My Tesla' to determine your battery cells temperature,
since this is your main worry.

Honestly, I don't think that using your home charger will create too much heat, like charging your phone.
The battery itself has its own heating management to prevent charging when the battery is below freezing.

This was not clear to me: Do you warm your whole garage to pre-heat the battery and your car,
or do you use your phone App to turn on the inside car heater?
If you can, try using a small electric heater inside your car connected to a socket in your garage to save battery energy.

I find it simpler to charge when the off-peak rate starts, so I know that the battery will be fully charged
the next morning, than to wait for the last minute, as power interruptions are possible or in case I need
to use my car for an emergency, like going to the nearest hospital or I receive an call from my work.

 

[dansev]

Unfortunately, I live in an urban area and have no garage. I’m fortunate to have a driveway, but no garage.

 

[RTPEV]

Others beat me to it, but just pre-heat the cabin for YOUR comfort and don't worry about the battery.

About the only scenario I can think of that would matter would be if you were on a road trip, pulled into a hotel with a low battery and needed to Supercharger first thing in the morning (you really should have charged before you parked the car overnight, but too late for that now!) You will almost certainly have a cold battery in the morning and will suffer slow charging speeds at your first charge of the morning, so if there were a way to pre-heat the battery while you were enjoying breakfast in the hotel, that would be great.

But for a daily commute? Don't worry about it at all!

 

[derotam]

Short story... you can't win...

Long story:
So it depends on what your goal is. Are you trying to save overall energy usage and use energy in the most efficient way possible, or are you wanting to get rid of the limited regen dots?

I guess you could also say that you want to get rid of the regen dots before your drive in the morning in the most efficient way possible.

The problem with all of this is that it takes A LOT to warm up a cold battery to where you wouldn't have a loss of regen.(obviously temperature dependent).

There are three options to get rid of the regen dots for you...have your car complete it's charge cycle just before you leave in the morning...but this is going to be temperature vs how much charging needs to be done dependent. This is also complicated by the fact that you have to guess when to start the charge based on the expected battery cooling for the expected nightly temperature.

Second, you could lower the charge rate and let it charge all night, again going to be temperature vs charging amount needed dependent. This is complicated by the fact that you have to guess the charging rate based on the expected temperature and its effect on the battery vs what charge rate will more than overcome that cooling loss.

Third, you can get in the car at some point prior to leaving and route to a supercharger and the car will start to heat up the battery. Again this is going to be temperature dependent and would take an unknown amount of time based on starting battery temperature...and you might have to stay in the car while it is doing it. Even if it will start heating while in park I think it will time out whether you are in the car or not.

 

[jrweiss98020]

When in doubt, RTFM. P. 75:

Tesla recommends activating climate settings at least 30-45 minutes before departure (see Climate Controls on page 124). Preconditioning times depend on outside temperature and other factors.

P. 77:

When parked, plug in Model 3 and use the Schedule settings, available on both the charging and climate control screens, to set a time when you want to precondition Model 3 (see Scheduled Charging and Scheduled Departure on page 165). Your vehicle determines the appropriate time to begin charging so it is complete during off-peak hours and the cabin and Battery are warm by your set departure time. For more information, see Scheduled Charging and Scheduled Departure on page 165.

 

[RTPEV]

Tesla recommends activating climate settings at least 30-45 minutes before departure (see Climate Controls on page 124). Preconditioning times depend on outside temperature and other factors.

30-45 minutes? I have yet to see my car take more than 5 minutes to get the "cabin temperature is at the desired setting" notification. And this even includes when I've been up north. Maybe not in below zero temps, but still...30-45 minutes?

 

[Randy-12]

The 30-45 minutes is when there is snow and ice accumulation

Model 3 Owner's Manual | Tesla

Understand various things you can do to ensure optimal performance in cold weather.

www.tesla.com

 

[RTPEV]

The 30-45 minutes is when there is snow and ice accumulation

Model 3 Owner's Manual | Tesla

Understand various things you can do to ensure optimal performance in cold weather.

www.tesla.com

That is helpful context!

 

[Watts_Up]

Unfortunately, I live in an urban area and have no garage. I’m fortunate to have a driveway, but no garage.

I would recommend using the phone App 'Scan My Tesla' to determine your battery cells temperature, since this is your main worry.
Using the Supercharger destination trick, you could then determine how long and much energy is required to warm up your battery.

Since you have a driveway, can you use a home charger?

 

[Darthbenji]

Let's say it's parked and unplugged and you need to supercharge. How do you warm the battery to optimal temperature for supercharging from the comfort of your home? The navigate to a supercharger doesn't work unless you're in the car.

 

[derotam]

Let's say it's parked and unplugged and you need to supercharge. How do you warm the battery to optimal temperature for supercharging from the comfort of your home? The navigate to a supercharger doesn't work unless you're in the car.

Not enough information. Whats the SOC, how far is it to the supercharger, how cold is it outside, what are you wearing?

I think the only way to warm your battery in that scenario would be to turn on cabin heat and set it to MAX. That will create the maximum possible discharge rate which will lightly warm the battery, and if you have the heat pump version vehicle, theoretically the car would route some of the excess heat to the battery, maybe.

Short answer would be you just wouldn't, you would go to the supercharger and let it charge however it is going to charge. If you were looking on getting up and doing a fast charge at a supercharger before your trip...then you have made poor planning decisions and should have left earlier to account for any increased supercharging time.

 

[vogz]

I've learned to not worry about the re-gen dots in the winter. I have a heated garage that I keep @ 60F and even sitting in there for a day or two the car will have re-gen dots @ 80-90% SOC.

After 3 winters of driving this car, I've realized that a cold battery doesn't really hurt my efficiency unless it's so cold that I use almost all or all re-gen. The heater usage (my 2020 doesn't have a heat pump) is a far greater drag on efficiency than a cold battery.

 

[GtiMart]

Preheating the cabin will at least bring the battery to around 10C if you give it enough time. It's better than nothing. You'll save a few minutes compared to just going to the SC, assuming it's close by and it's under freezing outside. I'll say like @derotam here, if you need to go to a SC in the morning on a cold battery, you haven't planned properly (in general). You'll need to spend more time charging.

The other two options I know of are the Ingenext Bonus module that has a precondition option, and the S3XY buttons which now have a precondition option too. I would think that both would require that you be in the car, probably in Drive, so they probably don't help you.

EDIT: Oh, I'll add one thing. IF you "drive it like you stole it" going to the SC you'll generate some heat in the motors/stators and in the battery that should also help.

 

[Regaj]

30-45 minutes? I have yet to see my car take more than 5 minutes to get the "cabin temperature is at the desired setting" notification. And this even includes when I've been up north. Maybe not in below zero temps, but still...30-45 minutes?

Yes, the cabin quickly comes up to temp, even if quite cold. But it takes much, much longer for a cold-soaked battery pack to increase temp.

Somewhat related... pre-conditioning with the Climate control will always condition the cabin. But it will only trigger heating of the pack (via sending power to the stator(s), which then heat the coolant, which then circulates and heats the individual cells) when it is below the BMS threshold.

Bottom line... the 30-45 minute recommendation by Tesla is to give the pack sufficient time to warm, not the cabin.

 

[DeltaOne]

Bottom line... the 30-45 minute recommendation by Tesla is to give the pack sufficient time to warm, not the cabin.

Interesting. It's kinda bugged me that Scheduled Departure finishes 30 to 60 minutes before the set time, but it makes sense that the car uses that time to warm the battery. You're right, the cabin warms up quickly.