Is leaving Tesla plugged in while not charging really beneficial?

[Undecided_2]

I plug in every day. I’ve had the MY since March and I’ve set the SOC at 60%. We’re set it that high as our parents are old and this gets us a big chunk down south to a supercharger on route. I have a Tesla Gen 3 charger wired into the house electric box on its own switch (upgraded metal box)

Scottish Power chaps and the charger install electricians who installed the charger, and the Power Distributor who replaced the head and added a 100amp fuse into the house told me that power surges are extremely rare. I also had a shut off switch between the head and the meter installed. He said if there’s a bad electrical storm then throw the switch if I was worried or unplug large stuff like the car. I don’t worry about it.

 

[ucmndd]

There’s no “battery health” reason to plug in at home if you charge at work every day, just like there’s no reason to plug in at work if you charge at home every day.

The only tangible benefit I can imagine is if you want to use shore power to precondition. But presumably you’re charging at work because it’s free / cheaper than charging at home, so not sure why you’d want to do this either.

 

[pepperoni]

There’s no “battery health” reason to plug in at home if you charge at work every day, just like there’s no reason to plug in at work if you charge at home every day.

The only tangible benefit I can imagine is if you want to use shore power to precondition. But presumably you’re charging at work because it’s free / cheaper than charging at home, so not sure why you’d want to do this either.

Exactly, that’s what I suspect. I’m just trying to understand the ”LEAVE YOUR VEHICLE PLUGGED IN when you are not using it” guidance. I’m thinking may be overcompensating for those folks who wait until their battery is nearly depleted to plug in, which is certainly not my case.

 

[ucmndd]

Exactly, that’s what I suspect. I’m just trying to understand the ”LEAVE YOUR VEHICLE PLUGGED IN when you are not using it” guidance. I’m thinking may be overcompensating for those folks who wait until their battery is nearly depleted to plug in, which is certainly not my case.

I suspect it’s mostly to break people from the ICE mentality you describe. Charge early, charge often.

There is also some benefit in the “edge case” sort of scenarios, mostly as a fail safe to keep you from depleting the battery. For example, one time my kid didn’t close a door all the way, which meant the car stayed on all night blasting the climate control. Whoops. Something like that could be problematic if you parked with a low SoC and weren’t plugged in. This particular example is somewhat mitigated now as the app will notify you if the climate control has been left on for a long tome, but that wasn’t always the case.

 

[jcanoe]

one time my kid didn’t close a door all the way

If you leave a door or window open for more than ~10 minutes after you park the Tesla Model Y can be set to send a notification to your phone via the Tesla app.

 

[ucmndd]

If you leave a door or window open for more than ~10 minutes after you park the Tesla Model Y can be set to send a notification to your phone via the Tesla app.

Right.

This particular example is somewhat mitigated now as the app will notify you if the climate control has been left on for a long tome, but that wasn’t always the case.

 

[Undecided_2]

I suspect it’s mostly to break people from the ICE mentality you describe. Charge early, charge often.

Interesting, you may be right. I used to drain my tank to about a quarter left and then fill it. But plenty of my friends drive until their car is running on fumes. Do that with an EV and you’ll be waiting some time to get the range back.

 

[ATPMSD]

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.

Let’s flip this question around. Assuming the EVSE is convenient to the car why not?

As as long as the SOC is not set to 100% there is no harm in leaving the car plugged in as this will keep the battery at your desired SOC. I used to allow my car to run down to about 50% before charging, but then one day my wife needed to take the car and the SOC was too low for her to make the trip comfortably - I don’t do that anymore.

 

[pepperoni]

Let’s flip this question around. Assuming the EVSE is convenient to the car why not?

As as long as the SOC is not set to 100% there is no harm in leaving the car plugged in as this will keep the battery at your desired SOC. I used to allow my car to run down to about 50% before charging, but then one day my wife needed to take the car and the SOC was too low for her to make the trip comfortably - I don’t do that anymore.

I believe I addressed my personal “why not” earlier in this thread, but I have one more to add. I prefer to charge at work since my company picks up the tab. Therefore, when I plug in my car after coming home from work, I need to reset the charge limit to prevent the car from also charging at home. Easier just not to plug it in at all. Yes it’s a minor thing and I would still plug it in at home if I could identify a good reason. I’m thinking in my case there is none.

 

[Undecided_2]

I believe I addressed my personal “why not” earlier in this thread, but I have one more to add. I prefer to charge at work since my company picks up the tab. Therefore, when I plug in my car after coming home from work, I need to reset the charge limit to prevent the car from also charging at home. Easier just not to plug it in at all. Yes it’s a minor thing and I would still plug it in at home if I could identify a good reason. I’m thinking in my case there is none.

I wouldn’t plug it in at home if I got free charging at work. I don’t plug mine in everyday at home - so far it’s been off of charge 3-days but I’ll plug it in before it gets to 20% which will take a while if I don’t drive anywhere substantial.

I believe the plug it all the time is to help people transitioning to EV from ICE as @ucmndd mentioned above. I really don’t believe we’ll damage the car by not plugging in every day. That would be very odd.

 

[ATPMSD]

I believe I addressed my personal “why not” earlier in this thread,

My response was not necessarily targeted at you, just approaching the question from a different direction.

 

[STS-134]

Let’s flip this question around. Assuming the EVSE is convenient to the car why not?

As as long as the SOC is not set to 100% there is no harm in leaving the car plugged in as this will keep the battery at your desired SOC. I used to allow my car to run down to about 50% before charging, but then one day my wife needed to take the car and the SOC was too low for her to make the trip comfortably - I don’t do that anymore.

I always keep the car plugged in at home, with the target charge level set to 50%. Even if the car was not driven since the last time it charged, it will "top off" the charge level to replace the small amount of self discharge over the past day. And in doing so, it also tops off the 12V battery which helps with its lifespan.

 

[jcanoe]

And in doing so, it also tops off the 12V battery which helps with its lifespan.

The Tesla Model Y will maintain, charge the 12V battery (now a 15.5V lithium battery module) as required whether or not the Tesla vehicle is plugged in.

 

[STS-134]

The Tesla Model Y will maintain, charge the 12V battery (now a 15.5V lithium battery module) as required whether or not the Tesla vehicle is plugged in.

Yes, it will maintain the small battery if it drops below a certain voltage threshold. But when the main drive battery is charging, it seems to top off the small battery regardless of its voltage. My PHEV does this too; whenever I charge the main drive battery, it applies between 13.8V and 14.2V to the 12V battery.

 

[jcanoe]

Yes, it will maintain the small battery if it drops below a certain voltage threshold. But when the main drive battery is charging, it seems to top off the small battery regardless of its voltage. My PHEV does this too; whenever I charge the main drive battery, it applies between 13.8V and 14.2V to the 12V battery.

My Model Y remains powered on when I charge at a public Level 2 charging station with Sentry mode active. I believe that when I charge at home with Sentry mode turned off that the Tesla Model Y does not always remain powered on during the charging session but could charge the 12V battery as needed during this time.

 

[dsnows]

I’m not a battery engineer, but my understanding is that battery degradation is due to discharging and charging. Electrons move from cathode to anode then have to be forced back to the cathode when charging, but the recovery is never 100%. Each cycle causes slight decrease in the charge capacity of the battery. It has to do with the physics of how batteries work. So, even losing a minimal charge over night means charging slightly more to get back to your baseline, and losing a tiny amount. The ideal situation would be to maintain a steady state of charge when not using the battery. Keeping it plugged in provides just enough energy to prevent the discharge therefore not have to recharge.

 

[android04]

If you charge at work everyday, then you don't have to plug your car at home everyday. The Tesla will charge the 12v battery, precondition the high voltage battery, and condition the cabin regardless of whether it's plugged into a wall outlet or not. It powers all of that through the high voltage battery. Being plugged into an outlet just serves to charge up the high voltage battery at the same time to maintain your set charge level.

Same thing goes for balancing and maintaining the cells in the battery pack. The car does this automatically above a certain charge level no matter if it's plugged in or not. But being plugged in helps top it back off to maintain your set charge level (balancing cells burns up a small amount of energy).

So don't overthink it if you charge at work everyday and have enough range to get to where you need to in case of emergency. I personally only charge at home and always plug the car back in as a matter of habit, even if I just drove it a few blocks away and it doesn't need the charge. It helps me to keep a routine so I don't forget to plug in after a long drive and then need the car for something urgent at a further distance.

 

[jcanoe]

I’m not a battery engineer, but my understanding is that battery degradation is due to discharging and charging. Electrons move from cathode to anode then have to be forced back to the cathode when charging, but the recovery is never 100%. Each cycle causes slight decrease in the charge capacity of the battery. It has to do with the physics of how batteries work. So, even losing a minimal charge over night means charging slightly more to get back to your baseline, and losing a tiny amount. The ideal situation would be to maintain a steady state of charge when not using the battery. Keeping it plugged in provides just enough energy to prevent the discharge therefore not have to recharge.

Lead-acid batteries benefit from being maintained at the correct float voltage to maintain the charge. Lithium batteries do not require a float voltage to maintain their charge. When plugged in, not actively charging, the Tesla vehicles does not draw any power from the grid. When Scheduled Charging is set up the Tesla Model Y draws a small amount of power from the grid until it is time to charge.

 

[DanDi58]

Tesla wrote that statement 10 years ago when owning an EV was new to most drivers.

I don't disagree but the OM has been updated hundreds of times so I would assume if this guidance was no longer appropriate, they would have taken it out. At any rate, everyone can do what they like. I plug mine in every night even if I haven't gone anywhere. I'm currently quarantining with Covid and the car is plugged in and will remain so. Battery level is set for 85%.

 

[Rocky_H]

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.

Yes, they needed to say that kind of thing a very long time ago because there was a lot of horrible misinformation out in the general public about electric cars that Tesla had to fight against and correct. There were two specific things:

1. It is actually safe to leave it plugged in if you want.

There was some very pervasive FUD that the cars could not stop charging on their own, and that being plugged in too long will just continue to "force feed" electricity into them until they explode in a fiery cataclysm and destroy the car and your house. This was based on a grain of truth from some legends of some very old, cheap, pathetic battery powered devices that didn't have any kind of battery monitoring and had some problems with overcharging. No electric cars have ever had that issue. And yes, we have seen threads created on this forum, where people are terrified, thinking they need to constantly watch the state of charge and run down to the garage in a panic to unplug the car before it blows up.

So they had to fight those fears by just letting people know they can plug it in as often as they want and leave it plugged in as long as they want and stop worrying about it.

2. Don't let the car run completely out or not have enough range.

This was kind of having to avoid bad PR and build good habits. They don't want people thinking they need to intentionally run it low, and then something happens, and someone forgets to plug in when they needed to, and then they don't have enough range to drive to work, and they throw a fit about what a finnicky piece of trash this electric car thing is, and they tell all their friends what a pain in the ass it is, and to never get one, etc. etc.

Tesla was trying to establish the market for a common usable consumer product electric vehicle. So they always want people to have the convenience of having enough range and being able to use the car often and happily. So it is better to recommend keeping it charged most of the time so they avoid those kinds of complaints.

So the recommendation in the manual is kind of a case of: "It isn't harmful to keep it plugged in a lot, so might as well do so." But the car can obviously go for a day or two at a time without charging with no issues at all. And plugging in unnecessarily is just putting a bit more work on the mechanical latch in the charge port for no reason, so if you really aren't wanting to charge at home, it's not really useful to plug it in there.