Battery Charging Best Practices

[OCR1]

I read through the Model 3 manual on battery charging and I did not see any guidance on best practices for charging. It mentions not to drain the battery to zero and to keep it plugged in as much as possible. But there is nothing about what max charge is best, whether to occasionally drain it down to 10% or charge it up to 100%, etc.

I’ve seen a lot of people post comments about best practices but has Tesla ever provided written guidance on this?

 

[Snow Drift]

Unless something has changed recently, the current thought is to charge up to 90% (unless you are going on a long trip).

If you set the car to above 90% you eventually get a warning message telling you to lower it.

If you set it to under 90% you may eventually see your potential mileage decrease due to a battery imbalance. Once you set it back to 90% for a while it will balance out and go back to 310 miles max (or 325 for you). This happened to me and others leading to Elon posting about a 90% daily charge vs. the old 80%.

As far as bottom range, try to keep it at 20% or higher.

 

[Rocky_H]

It's all pretty simple, but it's up to you to weigh your priorities. Lithium ion batteries last their best when they are kept near midpoint state of charge most of the time, so avoid sitting at 0% or 100% much and try to go more middle. But you also need to balance that with how much range you need to use from the car for it to be practical. Do you shoot for staying between 10-90? 20-80? Depends on how much you drive. If you're using a 90% charge limit, but you drive so little that you never really get much below about 70% before you're back home to recharge, then that 90% is probably a higher limit than you need, and you could go a little lower to be kinder to the battery long term.

 

[TexasEV]

Tesla doesn’t give “best practices” because if you follow the advice of plugging in when you can, the battery will be just fine no matter what you do. Just don’t let the car sit at 100% (you’ll get a warning message to discourage it). Tesla doesn’t want people obsessing over the battery as you’ll read many do here, and it’s just not necessary. All the theoretical issues you’ll read about here may be statistically significant but so small as to have no practical consequences for your use of the car. Let the battery management system manage the battery and have fun driving.

 

[TexasEV]

If you set it to under 90% you may eventually see your potential mileage decrease due to a battery imbalance. Once you set it back to 90% for a while it will balance out and go back to 310 miles max (or 325 for you).

No, it was the estimated range that was off, not the battery itself. State of charge can’t be measured directly. It’s estimated using an algorithm that may be more or less accurate at times. It’s not a balancing issue, it’s how the BMS estimates state of charge when it hasn’t been charged fully recently. The potential miles didn’t decrease, just the number that was displayed.

 

[ngogas]

90 percent. Plugged in Tesla is a happy Tesla.

 

[raptor5244]

So, if you don't drive a lot of miles each day is it still recommended to charge it back to 80-90% every night? For example, charge to 80%(250 miles) drive 10-15 miles or so a day and then then top it off a few days later or do you really have to put it back on the charger every night to top it off again? For those that don't drive a lot or have short commutes are we good with charging it once a week? Sounds like this will create less cycles, keeps battery between that 40-80% range for the most part.

 

[TexasEV]

What part of keep it plugged in and let the battery management system manage the battery do people not understand? You are not smarter than the car.

Don’t even think about it. Plug in when you get home. Unplug when you leave. It becomes a habit after a few days. You don’t need to think about your charge level, your car will always have a full (90%) charge.

Also what you’re describing is not a cycle. A cycle is a full charge/ discharge. And the charger is in the car, not the thing on the wall (UMC or Wall Connector).

 

[pdx_m3s]

Although 90% was recommended by Elon (take with a fine grain of salt), the “daily” range slider has a MAX daily range of 90%, going all the way down to 50% (I believe). I think you should pick somewhere in that range that best suits your average daily miles. A lower average state of charge (staying above 50%) is better for lithium ion batteries (this is settled chemistry), but how much so is up for debate.

FWIW, I drive 10-20 miles per day and I charge to 75% every night.

 

[MaryAnning3]

The 90% was recommended only after Telsa Kim managed to find a way to f up the state of charge (SoC) measurement by taking an extreme approach to following an earlier recommendation. The best practice is essentially 70%-30%. And, true, you do not have to follow the best practice. It is really no big deal if you don't.
But if you want to know what the best practice is, it is 70%-30%, or something close to that neighborhood. If you go on a trip every few months, charge to 90% just before you start. (Or just simulate a trip every 6 months or so to keep your SoC indication working okay.)
Pretty much all companies, Apple..., whose products involve Li-ion batteries avoid telling you best practices, presumably because they want their consumers experience to be pleasant and worry free. The truth is there is a "curve" that is very flat between about 70 and 30% for all Li-ion batteries and that is the best place to be for extended longevity. And you can ignore that at almost no peril, because your battery, in your car or computer or phone, is going to last a long time anyway.

 

[raptor5244]

[QUOTE="TexasEV, post: 3768074, member: 14218"You are not smarter than the car..[/QUOTE]

The machines have officially taken over.

 

[TexasEV]

The 90% was recommended only after Telsa Kim managed to find a way to f up the state of charge (SoC) measurement by taking an extreme approach to following an earlier recommendation.

Only if your understanding of history starts last year with the Model 3. The early Model S firmware had two charge settings, 92% and 100%. The 92% setting was recommended for daily use. The slider was introduced because for cars with two range settings EPA stupidly decided to report range as the average of the two. This happened with the Leaf. With the slider Tesla could report range as the range at 100% charge.

 

[timk225]

I charge to 90% and generally let it run down to somewhere around 20% to 30% before I plug it in again. That may take 1 day or 5, depending on what I'm doing. Once in a while, (every few months) I'll run it to 0 then charge it to 100% for balancing and to stretch the battery, keep it nice and flexible. I think 311 or 312 is the highest I've ever seen for total miles. 278-279 is my 90%.

 

[pdx_m3s]

I charge to 90% and generally let it run down to somewhere around 20% to 30% before I plug it in again. That may take 1 day or 5, depending on what I'm doing. Once in a while, (every few months) I'll run it to 0 then charge it to 100% for balancing and to stretch the battery, keep it nice and flexible. I think 311 or 312 is the highest I've ever seen for total miles. 278-279 is my 90%.

This is exactly what Tesla says not to do.

 

[Rocky_H]

I see people are yet again mixing up Tesla's sales-oriented recommendation with the scientific what is actually best for the battery. (@TexasEV ) The thing of keeping it at 90% all the time and keeping it plugged in all the time is for customer satisfaction of always having enough range, at the cost of a small penalty of it being a little bit worse for the battery's lifetime.

Tesla does not want to have to get into these kinds of long explanations and "it depends..." kinds of things with millions of customers, so they want to have one simple answer they can have their sales people give that is a pretty good answer that works fairly well for all circumstances. It's not the best for each person's scenario, but it's good enough.

 

[raptor5244]

This is exactly what Tesla says not to do.

Where does it say that and why is running the battery down to 20-30% before charge a bad thing? Isn't that what you are doing when you go on a trip? You start at 90% run it down fairly low charge, rinse repeat. My question is does it matter if this takes 5-10 days to get to 30% before charging?

I am mainly thinking about the health of the 12V battery, not main battery. In an ICE car the 12v battery gets topped off by the alternator when you drive. If you let an ICE car sit for 2 weeks you may not have enough juice to start the car. In the Tesla I am interested in understanding how the 12V battery is managed and charged. Does it only receive a charge when plugged in? Does the main battery charge the 12V battery automatically and if so does it wake itself up from sleep if the 12V battery is losing too much voltage. I know some are going to say just plug it in and don't worry about it but inquiring OCD folks like me want to know.

 

[Rocky_H]

I am mainly thinking about the health of the 12V battery, not main battery. In an ICE car the 12v battery gets topped off by the alternator when you drive. If you let an ICE car sit for 2 weeks you may not have enough juice to start the car. In the Tesla I am interested in understanding how the 12V battery is managed and charged. Does it only receive a charge when plugged in? Does the main battery charge the 12V battery automatically and if so does it wake itself up from sleep if the 12V battery is losing too much voltage. I know some are going to say just plug it in and don't worry about it but inquiring OCD folks like me want to know.

Ah. Then you need to be looking at threads about how the 12V battery is managed, not about charging practices for the car.

What charges the 12v battery and when?

Any reason not to hook up a battery tender to the 12 volt battery ?

When does 12V battery actually get charged

 

[CravenRx]

I charge to 80% because at 90% it seems like the regen breaking is limited for about half my drive to work. At 80% I get full regen by the end of my street. Is this a bad idea? Just seemed like it would be more efficient if I used the hills around my house to charge the battery a little.

 

[TEG]

Another thought:

Performance can vary based on SoC (State of Charge). If you want max acceleration, you want a higher SoC.

 

[TEG]

I am mainly thinking about the health of the 12V battery, not main battery. In an ICE car the 12v battery gets topped off by the alternator when you drive. If you let an ICE car sit for 2 weeks you may not have enough juice to start the car. In the Tesla I am interested in understanding how the 12V battery is managed and charged. Does it only receive a charge when plugged in? Does the main battery charge the 12V battery automatically and if so does it wake itself up from sleep if the 12V battery is losing too much voltage. I know some are going to say just plug it in and don't worry about it but inquiring OCD folks like me want to know.

Also, something else to keep in mind is that "best practices" for a lead/acid battery (the 12v) is totally different from lithium ion.
The 12v lead/acid would love to be kept at max SoC all the time and never required to get drained. Letting a lead/acid battery run down to near empty is terrible.

Lithium-ion, on the other hand, really doesn't want to stay "topped off" near 100%. It is damaging to be "fully charged" like that. As others have said, it would rather be kept around 50% SoC most of the time.
But you want to have some useful range available, and probably don't want to have reduced performance, so starting out regularly at 80% or 90% is a good compromise of not hurting the battery too much, and making it as useful to you as possible.

Then there is the whole thing about the Lithium-ion battery management computer(s) and the data it keeps on what it thinks is going on with the battery. If you don't go from near empty to near full once and a while it can start to get confused about how much capacity and range is possible. And different modules can drift out of balance. So I think it is considered a good idea to do a "full cycle" (maybe from 10% to 100%) once and a while just so the computer(s) can optimize the battery. And then drive the car soon after getting to 100% so it does't stay fully charged too long. Personally, I plan on doing something like that no more than maybe once a year.