Is leaving Tesla plugged in while not charging really beneficial?

[pepperoni]

Yes, I know this question has been asked before, but I have seen no satisfactory answers to this question. The user manual states:

The most important way to preserve the high voltage Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it.

And yes, the bold and all caps is in the manual, suggesting that this is a very important step for battery preservation. I can understand the rationale for plugging in when the car will not be used for an extended period of time (i.e., preventing the batter level from getting too low), but does plugging in every night, even when no charging is planned, really helpful?

I have the luxury of being able to charge at work, so almost never charge at home. It feels a bit silly to plug in my car for the evening when no charging is planned. Furthermore, plugging in isn’t without risk (power surges, fires). I would prefer just not to plug it in, but that goes against the guidance in the manual.

Does anyone have any real insight into why Tesla recommends plugging in whenever the car is not in use? For someone in my situation, is there really any benefit?

 

[thesmokingman]

Should I wait for the battery to fully deplete before charging?
Tesla uses lithium ion batteries so there is no memory effect, this means there is no need to deplete the battery before charging. We recommend plugging in as often as possible.

^^Per Tesla

Further reading...

Long term being away, plugged or unplugged?

Hi guys, So…I will be out of the country for a good 6-10 months depending on the assignment situation. No one will have access to my garage to help charge or drive around when I’m away so I have few questions regarding my M3P 1: will the car will be drivable after I return without needing any...

teslamotorsclub.com

 

[GtiMart]

I believe the benefit is that the car will never fall down to 0% SOC. Whatever happens to the car, even if it wastes a lot of power, it will always be able to charge (up to your set SOC) because it's plugged. You can forget it for months, nothing bad will happen.

 

[mangrove79]

Yes, I know this question has been asked before, but I have seen no satisfactory answers to this question.

We need someone who understands the physics of battery technology to chime in, but I agree that it's hard to find a good answer on this forum if it exists. I'm in the habit of leaving it off the charger when I'm not planning to charge. I ended up plugging it in about once a week, and so far in 12 months, my battery hasn't degraded that much, maybe 2%. I also found that the electricity usage in the first couple of months when I was following Tesla's recommendation was really high, suggesting significant energy loss when plugged in (not charging).

 

[thesmokingman]

I believe the benefit is that the car will never fall down to 0% SOC. Whatever happens to the car, even if it wastes a lot of power, it will always be able to charge (up to your set SOC) because it's plugged. You can forget it for months, nothing bad will happen.

It's a lot more than the the obvious. Plugging in everyday reduces the load on the HV battery because it is not burdened by maintaining the LV battery. The HV battery is used to charge the LV battery, so when it's plugged in it uses AC to maintain instead of the HV battery.

 

[TunaBug]

And yes, the bold and all caps is in the manual, suggesting that this is a very important step for battery preservation.

Maybe it's bold because they're just tired of people asking the question?

 

[jcanoe]

The most important way to preserve the high voltage Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it.

Tesla wrote that statement 10 years ago when owning an EV was new to most drivers. Every Tesla owner's situation is unique. Some have no way to charge at home. Some only charge at work. When you leave the Tesla vehicle at the airport you may be away for several days or weeks with no way to plug in the Tesla vehicle. When you are on a trip the only charging option may be to use a Supercharger. In many cases you can't leave the Tesla vehicle parked at the Supercharger without incurring idling charges.

As long as you are aware that at least every few days the Tesla vehicle needs to be plugged in to charge the Tesla vehicle and the lithium battery will be fine. If you would rather not have to think about whether you remembered to plug in the Tesla vehicle just make it part of your daily routine when you arrive home at the end of each day.

 

[Benito1283]

It's a lot more than the the obvious. Plugging in everyday reduces the load on the HV battery because it is not burdened by maintaining the LV battery. The HV battery is used to charge the LV battery, so when it's plugged in it uses AC to maintain instead of the HV battery.

I don't believe this is true. Even when plugged in, the HV battery is used to charge the LV battery. If enough LV charging happens and the SOC drops, then the HV battery will get topped off via AC power. But AC power isn't used when the car periodically wakes up to charge the LV battery. I know this because a) the lights on the charger don't blink, and b) I've confirmed this by measuring the amps with a clamp-on multimeter when it's charging the LV battery; there's no current.

So in the end, having it plugged in doesn't bypass the usage of the HV battery for LV charging, which is too bad. I assume there's a reason.

I also don't believe AC power is used to run the air conditioning when Cabin Overheat Protection is activated, which is also too bad. However, AC power is used when using climate/preconditioning while plugged in. That's the main reason I typically leave it plugged in even when not charging - to use AC power instead of range to heat/cool the car before driving.

 

[Tman317]

Tesla wrote that statement 10 years ago when owning an EV was new to most drivers. Every Tesla owner's situation is unique. Some have no way to charge at home. Some only charge at work. When you leave the Tesla vehicle at the airport you may be away for several days or weeks with no way to plug in the Tesla vehicle. When you are on a trip the only charging option may be to use a Supercharger. In many cases you can't leave the Tesla vehicle parked at the Supercharger without incurring idling charges.

As long as you are aware that at least every few days the Tesla vehicle needs to be plugged in to charge the Tesla vehicle and the lithium battery will be fine. If you would rather not have to think about whether you remembered to plug in the Tesla vehicle just make it part of your daily routine when you arrive home at the end of each day.

I agree, The important thing is don't let the battery run totally down so if you don't drive often and might forget to charge it's better to keep it plugged in at home. I'm retired and don't need to charge daily. I charge every 2-3 days to 80% and wait until I'm down between 40-55% before plugging in. That works for my particular situation. If I was going away for a few weeks I would keep it plugged in.

 

[thesmokingman]

I don't believe this is true. Even when plugged in, the HV battery is used to charge the LV battery. If enough LV charging happens and the SOC drops, then the HV battery will get topped off via AC power. But AC power isn't used when the car periodically wakes up to charge the LV battery. I know this because a) the lights on the charger don't blink, and b) I've confirmed this by measuring the amps with a clamp-on multimeter when it's charging the LV battery; there's no current.

So in the end, plugging it in doesn't bypass the usage of the HV battery, it just lets it automatically top off the charge when it needs to. Although it would be smart if they made the LV battery charge via AC. I also don't believe AC power is used to run the air conditioning when Cabin Overheat Protection is activated, which is too bad. However, AC power is used when using climate/preconditioning while plugged in.

I think you're right. I went back to the posts regarding this and couldn't find an official source.

 

[EVEnergy]

Your car's BMS constantly manages voltage across the battery packs and it's my understanding that by plugging in, the car can use "house power" to help maintain voltage and temperatures in the pack. If you don't plug in, it will use the internal power which is not as efficient. Also, if you pre-heat/condition your car before you leave the house, it will use the house power to do that rather than waste your battery power.

 

[Benito1283]

Your car's BMS constantly manages voltage across the battery packs and it's my understanding that by plugging in, the car can use "house power" to help maintain voltage and temperatures in the pack. If you don't plug in, it will use the internal power which is not as efficient. Also, if you pre-heat/condition your car before you leave the house, it will use the house power to do that rather than waste your battery power.

If that's in fact true that AC power is more efficient in maintaining voltage and temp than battery power, that's a great reason to leave it plugged in.

 

[jcanoe]

Your car's BMS constantly manages voltage across the battery packs and it's my understanding that by plugging in, the car can use "house power" to help maintain voltage and temperatures in the pack. If you don't plug in, it will use the internal power which is not as efficient. Also, if you pre-heat/condition your car before you leave the house, it will use the house power to do that rather than waste your battery power.

The Tesla vehicle will not warm the battery while the Tesla vehicle is plugged in unless charging and the battery is too cold to charge or while preconditioning. It would just waste energy to maintain the battery temperature when the vehicle is parked.

 

[bluetrep1]

the only purpose is to cover up the phantom drain.

 

[Undecided_2]

the only purpose is to cover up the phantom drain.

Phantom drain?

 

[WindPower]

Phantom drain?

Phantom drain is the loss in battery charge when the car is idle. With sentry mode on (cabin monitoring), my Y loses 4% charge overnight (park at 7:30pm with 52% when I get home from work, get on the road next morning at 9am with 48% state of charge). Turn monitoring off and phantom drain drops to 2%. Turn off the Tesla app on my iPhone and phantom drain drops to maybe 1%.

So when I go to the airport, I turn off monitoring and close the Tesla app.

 

[Undecided_2]

Ah okay. If I leave it in the garage with everything off the battery barely loses anything over a week.

However, occasionally, it randomly turns on the climate control for no reason during the night and I’ll get an alert that the climate was running for ~3 hours - outside temp is barely above 12c and cabin about the same, and I can’t work out why. I can’t be faffed to call Tesla as I’m not awake when it happens.

But I suppose that’s not phantom drain.

 

[pepperoni]

Thanks for all the feedback! I found the response from @jcanoe interesting, who noted that this guidance has been in the manual for 10 years. I’m sure a lot has changed in the power system software in that time. Although I haven’t seen a definitive explanation (yet) on why this guidance exists, the most likely explanation posited by a few of you is that it prevents the situation where someone doesn’t plug in their car for an extended period of time while the battery slowly drains itself.

I’m still not grasping the importance of leaving my car plugged in when I have no plans to charge. Several replies above stated that the car can use AC rather than battery for various functions, but I admit I’m a little skeptical. When I’m not charging, the charger reports 0 Amps 2 Volts when it is awake, and then the car sleeps most of the night. I’ve set up the Teslamate datalogger for the past month, and see no evidence of AC use overnight. I don’t precondition the climate in the morning. The observation by @Undecided_2 above that climate control sometimes comes on at night is interesting. Maybe AC power gets used then? I’ve owned my car less than 2 months, so perhaps I haven’t seen these events.

In any case, I think I will only plug in my car overnight when I plan to charge. I have yet to see a good definitive reason why I should plug in every night. Too bad there aren’t any Tesla engineers posting on this topic, since it is a common question that would be easy to clear up.

 

[Benito1283]

Several replies above stated that the car can use AC rather than battery for various functions, but I admit I’m a little skeptical.

AC power is definitely used to precondition and use climate when plugged in. Not sure why you’re skeptical of that. If you ever use that feature that may be a reason to plug in.

In any case, I think I will only plug in my car overnight when I plan to charge.

Is there a downside to plugging it in every night? There may be reasons for Tesla’s recommendation we just don’t fully understand.

Even if you don’t, your car will be just fine.

 

[pepperoni]

@Benito1283, I should have clarified that I have no reason to doubt the car will use AC to precondition the battery or set climate prior to departure. I don’t use these features, as I live in a temperate climate. I am skeptical that my car is using AC overnight when it is not charging.

The downsides to plugging in overnight are minor. A power surge is probably the biggest reason, but the wear and tear on the charging port and just the general hassle for a presumed useless activity are also factors. But I’m willing to do it if I can discover a good reason.