Warning for those charging using 120v

[Lemonpie889]

So, I learned something quite interesting today that I thought would be helpful to share. I have a LR RWD with only 7K miles. Just recently, I noticed that my 90% SOC was decreasing every day by 1 mile (from ~290 to now ~287). I knew that this couldn't be battery degradation given how few miles I have on the car. I scheduled a service appointment to see what was going on. I received a text from the SC today providing a potential explanation.

The SC told me they checked my battery remotely and confirmed that it was still in good health. They noted, however, that the battery was subject to "poor charging habits." I thought the comment was strange given that I always set my charging limit to 90% and plug in as often as possible (per the owner manual's instructions).

However, what I began to realize is that because I use the 120v outlet to charge at home (~5 mi/hour), I more often than not do not get a full 90% charge overnight (because my commute is >40 miles and the 120v is so slow). The SC informed me that when I charge in "short bursts" like this, the battery can become "unbalanced," and lose track of the battery's true charging capacity.

As a solution, the SC recommended that, from now on, I charge to 90% as often as possible. To recalibrate, the SC also told me to leave the charger plugged in for 1-2 hours after reaching a 90% SOC. The SC stated it may take 4-6 weeks for the battery to start going back up, but that they have seen success with this recalibration method.

So, all that is to say: for those of you using 120v to charge on a daily and/or consistent basis, charge to 90% as often as possible; if not, attempt to find a different charging solution (e.g. installing a 240v). If you've experienced "degradation" try recalibrating by leaving the car charged in at 90% for 1-2 hours consistently for several weeks. Or, try charging to 100%, draining to ~10%, then charging back up to 100%, and then driving down below 90%.

 

[Tam]

...The SC informed me that when I charge in "short bursts" like this, the battery can become "unbalanced," and lose track of the battery's true charging capacity...

i assume charging with 240V would shorten the charge duration while charging with 120V would have a longer duration and not "short bursts".

Would someone please expand on this undesirable "short bursts" charging?

 

[Lemonpie889]

To clarify, by short bursts I mean plugging and then unplugging before the car gets to 90% SOC frequently. This shouldn’t be a problem for the average commuter/driver as most people plug in overnight and wake up to a full charge. I was not as the 120v wasn’t giving me enough miles to make up for my daily driving habits.

 

[pdx_m3s]

What I take away from this is that the battery management system is still “working” the battery (balancing, calibrating, etc) even after a charge is completed, so it’s best to ensure a couple hours of buffer between charge completion and unplugging.

 

[Tam]

...I mean plugging and then unplugging before the car gets to 90% SOC frequently...

Thanks for the clarification. That does make lots of sense.

Because 120V takes too long to get to 90% so it's not achieving 90% goal daily if an owner has a long commute.

 

[Tam]

What I take away from this is that the battery management system is still “working” the battery (balancing, calibrating, etc) even after a charge is completed, so it’s best to ensure a couple hours of buffer between charge completion and unplugging.

What I understood from the thread is if I want an accurate battery gauge, I need to charge to 90% daily.

Thus, charging to 80%, 70%, 60% daily might give out reading as if the battery has lost range but actually, it's just the inaccurate calculation.

 

[pdx_m3s]

What I understood from the thread is if I want an accurate battery gauge, I need to charge to 90% daily.

Thus, charging to 80%, 70%, 60% daily might give out reading as if the battery has lost range but actually, it's just the inaccurate calculation.

That too. I only use 5-10% of my SR+ range daily so I charge to 70% every night.

 

[ewoodrick]

So, my take is that this is simply a bad indication and not given the batteries a chance to equalize.

I dare say that if you charge to 80 or 90% and then periodically, every few months, let it got to 100% and stay there for a little, that you'll battery will be happy.

I think that the SC was stretching it a little when the blamed it on the short cycles (which is kinda stupid, since I'm assuming that they were actually long cycles at slower speeds).

My numbers are still showing great after a year and I generally go to 100% just by having a trip to go on and charging to 100% before a trip.

Basic rules from my playbook.

• Don't charge to 100% every day, unless you absolutely need to do so, because you drive that far.
• Don't take it to near 0% to try to balance the batteries, that's old school concepts. Of course, like above, it's okay if you need to because of drive.
• 80-90% is probably some of the better places to charge to,
• Charge to 100% every few months.
• Stop worry about the battery so much!

 

[JulienW]

...let it got to 100% and stay there for a little, that you'll battery will be happy.....

Lit-ion's don't like being at full charge. This is extremely stressful on the battery. If you must charge to 100% you should start to discharge ASAP to avoid battery degradation.

https://batteryuniversity.com/index.php/learn/article/how_to_prolong_lithium_based_batteries

 

[duanra]

That too. I only use 5-10% of my SR+ range daily so I charge to 70% every night.

Same, and when at home, I leave the connector plugged in. I don't see unplugging it beneficial by the way. It is actually the opposit recommended by the manual.
Also, be carefull, not everyone is knowledgable in the SCs or at customer support answering the phone.
I've been told that the Model 3 cannot rust cause it is in aluminum. The agent was surprised when I informed him that only part of it was in aluminium.
Also once, CS sent me a screen shot of the app to explain me something not applicable to my car cause it was a Model S screen shot. So again, take everything you are being told with a grain of salt.

 

[pdx_m3s]

Same, and when at home, I leave the connector plugged in. I don't see unplugging it beneficial by the way. It is actually the opposit recommended by the manual.

Agreed. My SR+ is plugged in at least 12 hours overnight. I have charging set to begin at 2am, and it takes but an hour or so to fully charge to 70% on my 30 amp 240 circuit.

 

[stonelance]

There are other threads on this and I believe it is pretty well understood. The issue is that you are charging a small percentage of the battery in each charge session. Even with 240v and letting it charge to 90% and stay plugged in, this happened to me. It was because i have a short commute and would only use 5% each day. The solution was to not plug in every day, and instead only plug in when my soc is lower, like 50% or less, then let it charge up to 90. Now I usually don't bother plugging in all week and just plugin at the end of the week so I have a full charge for the weekend. Of course that isn't really an option when you only have a 120v charge option though.

 

[Dogtone]

The solution was to not plug in every day, and instead only plug in when my soc is lower, like 50% or less, then let it charge up to 90. Now I usually don't bother plugging in all week and just plugin at the end of the week so I have a full charge for the weekend

I am a newer Model 3 owner that does not put a lot of miles on my car. I am finding the above method is working for me.

 

[Lemonpie889]

There are other threads on this and I believe it is pretty well understood. The issue is that you are charging a small percentage of the battery in each charge session. Even with 240v and letting it charge to 90% and stay plugged in, this happened to me. It was because i have a short commute and would only use 5% each day. The solution was to not plug in every day, and instead only plug in when my soc is lower, like 50% or less, then let it charge up to 90. Now I usually don't bother plugging in all week and just plugin at the end of the week so I have a full charge for the weekend. Of course that isn't really an option when you only have a 120v charge option though.

How do we reconcile this with the manuals recommendation to plug in as often as possible?

“The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model 3 for several weeks. When plugged in, Model 3 wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.”

The manual also says that the soc of charge prior to charging the battery does not affect battery health.

“There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly.”

Also from Tesla’s battery faq section.

“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.”

The point is, I don’t think waiting to get to a certain % before plugging in matters. What seems to be important, however, is minimizing the frequency with which you unplug before allowing the battery to go 90%. Again, this sounds like it shouldn’t be a problem for most people because they are able to achieve a full 90% charge overnight (regardless of the charging method used).

 

[srs5694]

How do we reconcile this with the manuals recommendation to plug in as often as possible?

As somebody who's written technical documents for a living (I've written over 20 books on Linux and related software), I can assure you that they leave out a lot of details. By all accounts, maintaining optimum battery health is a complex topic. An EV's battery management system (BMS) includes programming to deal with the most technical issues, but if there'll be some subtle effect of doing X vs. Y, the manual is likely to pick the simpler of those two solutions. Likewise, it'll try to consolidate as many pieces of advice into one simpler piece of advice as possible.

That's not to say that I have affirmative knowledge that owners should follow different specific charging schedules in different specific situations. I'm just saying that any EV's owner manual will be written for a general audience and may gloss over or omit details that owners might find confusing or off-putting, so long as the simplified advice in the manual wouldn't cause serious problems (like an increase in warranty claims).

Looked at another way, Teslas are owned by a variety of people with different driving habits and different charging facilities. Some Tesla owners live in apartments and can charge only on a more sporadic schedule than others. Some take frequent long road trips and so make heavy use of Superchargers. Some have short commutes, and others long commutes. The car must be engineered so that the battery holds up reasonably well for all of these use cases; otherwise, Tesla will end up doing a lot of costly in-warranty battery replacements in a few years. That's not to say that certain practices won't be better than others, but IMHO, some posters on this forum are too rigid in recommending particular practices.

 

[kavyboy]

...Or you can just plug it in when you can at 90% and not worry about it.
To me, it's like discussing strategies for how to fill up your gas tank. What temperatures make the fuel more dense and when should you pump? How do you reduce water condensation in the tank? Do you fill up more frequently to reduce vapor space, or do you let it run down to keep sludge from accumulating? Do you top off? Etc., etc. Just doesn't matter, for the most part.

 

[JulienW]

...By all accounts, maintaining optimum battery health is a complex topic....

....with many variables that can't be covered, some unknowns and lot of "if this (happens) then that (is effected)".

 

[duanra]

As somebody who's written technical documents for a living (I've written over 20 books on Linux and related software), I can assure you that they leave out a lot of details. By all accounts, maintaining optimum battery health is a complex topic. An EV's battery management system (BMS) includes programming to deal with the most technical issues, but if there'll be some subtle effect of doing X vs. Y, the manual is likely to pick the simpler of those two solutions. Likewise, it'll try to consolidate as many pieces of advice into one simpler piece of advice as possible.

That's not to say that I have affirmative knowledge that owners should follow different specific charging schedules in different specific situations. I'm just saying that any EV's owner manual will be written for a general audience and may gloss over or omit details that owners might find confusing or off-putting, so long as the simplified advice in the manual wouldn't cause serious problems (like an increase in warranty claims).

Looked at another way, Teslas are owned by a variety of people with different driving habits and different charging facilities. Some Tesla owners live in apartments and can charge only on a more sporadic schedule than others. Some take frequent long road trips and so make heavy use of Superchargers. Some have short commutes, and others long commutes. The car must be engineered so that the battery holds up reasonably well for all of these use cases; otherwise, Tesla will end up doing a lot of costly in-warranty battery replacements in a few years. That's not to say that certain practices won't be better than others, but IMHO, some posters on this forum are too rigid in recommending particular practices.

You have some points i like.
The way i see it : Tesla guarantees that your battery will hold up 70% of it charge in 8 years. If not, they will replace it. (unless i misunderstood). So even if 90% is harder on the battery than 80% for instance, Tesla will recommend 90 as long as the battery won't degrade bellow 70. However it might be better to keep it under 80 if it fits your commute. Now even if keeping the battery at a low soc means unbalanced battery, I'd rather have an unbalanced battery than a drgrades battery since you can balance your battery but not "undegrade" your battery.
Of course all this blurb is just speculation from me, however it seems logic !

 

[COrocket]

...Or you can just plug it in when you can at 90% and not worry about it.
To me, it's like discussing strategies for how to fill up your gas tank. What temperatures make the fuel more dense and when should you pump? How do you reduce water condensation in the tank? Do you fill up more frequently to reduce vapor space, or do you let it run down to keep sludge from accumulating? Do you top off? Etc., etc. Just doesn't matter, for the most part.

That’s a pretty good analogy. The amount of people that worry when their battery charges +/-5 miles on a full charge is weird.

 

[djroberts]

That too. I only use 5-10% of my SR+ range daily so I charge to 70% every night.

I'm not an expert but curious where you got that number? There are optimal ranges for lithium batteries. My experience is in the RC field and 70 might be too low for a battery in active use. I think between 80-90 is ideal. Take it with a grain of salt. These batteries are different than the ones I've used.