# Optimizing battery charging



## Bikertodd (6 mo ago)

I have read lots of stuff about how charge for optimum battery life. One person suggested that charging the battery at around 50% capacity is the least damaging to the battery. Letting the battery drop to 10% or charging in the 90% range contributes more to battery aging than charging around 50%. Is this true? I don’t know.

Let me ask about a more specific scenario. Let’s say I only drive around 30 miles/day. That is around 10% of my 300 mile range, so I could choose to charge to 60% and run it down to 50% each day, then charge back to 60%. This is scenario one. Scenario two is to charge to 80%, run the car for six days down to 20% and then charge back up to 80%. Assuming it looses a bit each day sitting in the garage, maybe I have to charge it every five days instead of six. So which scenario is easier on the battery, Scenario one or two?


----------



## JasonF (Oct 26, 2018)

I can't say if my battery has the least degredation or not, but it's 4 years old and had daily charging to 90%, and I haven't had any really obvious problems with it.


----------



## Ed Woodrick (May 26, 2018)

What about reading the manual and stop listening to all the armchair experts.
Only rule, don't charge to 100% daily.


----------



## Power Surge (Jan 6, 2022)

You're overthinking the subject, as we ALL do at first. 

Here's my personal opinion.... The ONLY agreed upon thing that damages the battery, is charging to 100% and letting the car SIT like that for extended periods (well also letting it sit at close to zero as well). 

Beyond that, there's no real evidence that any specific charging habit causes any issues. Me personally? I charge to 80% every day, even though I only use 30%. If I know I'm going on a long trip, then I'll charge higher. 

The only other thing to note, is that whatever method you choose, it's still good to let the car do a 90% to 10-15% cycle a few times now and then, because that helps keep the BMS calibrated.


----------



## DocScott (Mar 6, 2019)

Power Surge said:


> Here's my personal opinion.... The ONLY agreed upon thing that damages the battery, is charging to 100% and letting the car SIT like that for extended periods (well also letting it sit at close to zero as well).


I...don't agree with that. 

I've discussed it in other threads; I am not at all sold that charging the car to full and letting it sit is any different from charging it to full and driving it right away. The idea that it's worse seems to come from studies of _keeping_ lithium batteries charged at 100% by continually trickling charge into them. That's understandably pretty bad for a battery. But I've seen no evidence (or convincing mechanistic explanation, for that matter) that letting a car that's fully-charged sit causes additional degradation.


----------



## garsh (Apr 4, 2016)

DocScott said:


> I've discussed it in other threads; I am not at all sold that charging the car to full and letting it sit is any different from charging it to full and driving it right away. The idea that it's worse seems to come from studies of _keeping_ lithium batteries charged at 100% by continually trickling charge into them. That's understandably pretty bad for a battery. But I've seen no evidence (or convincing mechanistic explanation, for that matter) that letting a car that's fully-charged sit causes additional degradation.


You're correct in that nobody has run that particular test. However, Tesla states in several different ways that you should not generally charge to 100%. When a Tesla reaches the desired charge level, it doesn't continuously trickle-charge - it waits until the charge has dropped 2-3% before boosting it back up. So it would seem that Tesla is saying that charging to 100% - even if leaving immediately after reaching 100% - is not particularly good for battery health.

Here's their "Range Tips" page. It says that you should generally charge to 90% (unless you have an LFP battery). They don't say why, which is frustrating.








Range Tips | Tesla Support


Your Tesla vehicle continuously monitors its energy level and proximity to known charging locations to provide range assurance. To maximize efficiency, it is important to know the factors that impact range and the recommended ways to reduce energy consumption.




www.tesla.com





Here's the message that pops up if you charge to 100% twice in a row. Here, it specifically says that doing so will "shorten battery life". To get this to appear, I charged to 100% two days in a row, each time leaving within 30 minutes of charging ending. So it's not necessary to leave the car sit at 100% for very long as far as Tesla is concerned.









The Owner's Manual frustratingly doesn't say anything about charging to only 90% or avoiding 100%. However, it does specifically point out that you should charge to 100% if you have an LFP battery. Which implies that you probably shouldn't if you don't have an LFP battery:








Model 3 Owner's Manual | Tesla


Learn about your vehicle’s battery and battery best practices.



www.tesla.com


----------



## JasonF (Oct 26, 2018)

garsh said:


> Here's the message that pops up if you charge to 100% twice in a row. Here, it specifically says that doing so will "shorten battery life". To get this to appear, I charged to 100% two days in a row, each time leaving within 30 minutes of charging ending. So it's not necessary to leave the car sit at 100% for very long as far as Tesla is concerned.


I know people have told me that laptop batteries are nothing at all like car batteries, but they do have similar chemistry. What damages laptop (and tablet) batteries is continually keeping them at 100%. Apple even dove into promoting battery safety by "holding" charge and refusing to go back to 100% if the charging system knows it's plugged in most of the time (you can still force it to 100%).

From that comparison I don't believe the assertion that if you charge to 100% once, or charge to 100% and let it sit overnight before leaving for a trip, that you've already destroyed your battery - I think it requires a pattern. And note that pattern is possible accidentally, if you're someone who drives long distances a lot and charges to 100% two or three times a week.


----------



## Harriscott (Apr 16, 2021)

I prefer your first scenario (charge to 60% daily) to the second. Plugging in every time makes for a simple habit with lower chance of annoyance due to low SOC. I do this now, but it used to be 70% (which Jeff Dahn recommended once) back when I did L3 charging.

It appears that staying near 50% is good, smaller SOC swings are better, and L1/L2 charging is better. E.g. you should never supercharge, not even once  

It also appears that such things have little correlation with battery health. So this is really for entertainment purposes. The car seems zippier at 90% than at 60%. And supercharging is great (except for the time or two I didn't back enough to reach the charging cable. How embarrassing.)


----------



## garsh (Apr 4, 2016)

JasonF said:


> I don't believe the assertion that if you charge to 100% once, or charge to 100% and let it sit overnight before leaving for a trip, that you've already destroyed your battery


Tesla only says that it "shortens battery life". That's quite different from "destroys the battery".


----------



## tivoboy (Mar 24, 2017)

Scenario two.


----------



## android04 (Sep 20, 2017)

I recommend a scenario where you plug in every day out of habit. That way you don't forget or get distracted some day and end up with a really low charge as you are ready to go to work


----------



## JasonF (Oct 26, 2018)

garsh said:


> Tesla only says that it "shortens battery life". That's quite different from "destroys the battery".


That's not from Tesla, mostly it's people who translate it to mean you'll destroy your battery if you let it hit 100% for any length of time, and then scold other people for it. Sometimes they even add a wide margin to the scolding and tell people anything over 80% is dangerous.

And that's particularly funny, because when Apple throttles the laptop battery charging, it halts anywhere between 80% and 95%. If they would believe above 80% with their laptop batteries is dangerous, why would they ever allow it to go over that?

Speaking of which, what I learned from Apple's tablet batteries is that when you let them hit 100% and keep them there, a tiny bit of hydrogen is released. The hydrogen comes from the battery chemistry itself, which is how it gets "diminished" at 100%. Most of the time the hydrogen is re-absorbed when you drain the battery, but each time you charge to 100% and keep it there, more hydrogen is produced until it can't be reabsorbed anymore - and then at some point one cell is missing enough chemistry that you have a failed cell (and it puffs up like a balloon).

I'm guessing the Tesla battery cells are somewhat the same since they have similar chemistry, except they're basically "deep cycle" optimized while a laptop/tablet battery wouldn't be. Even so, I bet at its extremes of charge (100% and 0%) it behaves much the same way.

LFP batteries are strange. I read about them, and that they like being "fully charged" because unlike standard lithium cells that hold energy until they're bursting at the seams (literally, with hydrogen) the LFP cells won't hold that much. So when they're at 100%, they're not really at 100%. The penalty is you need more cells for the same range, and they can't discharge as fast.


----------



## bwilson4web (Mar 4, 2019)

My understanding is at peak voltage, it tends to convert some of the lithium into inert compounds. But lower voltages have a lower conversion rate.

My practice is to daily run about 2/3 SOC and use 100% for the first segment of a cross country the next day. My 76,000 mi, March 2019, 240 mi new battery is now down to 219 miles at 100% SOC.

Bob Wilson


----------



## DocScott (Mar 6, 2019)

DocScott said:


> I've discussed it in other threads; I am not at all sold that charging the car to full and letting it sit is any different from charging it to full and driving it right away. The idea that it's worse seems to come from studies of _keeping_ lithium batteries charged at 100% by continually trickling charge into them. That's understandably pretty bad for a battery. But I've seen no evidence (or convincing mechanistic explanation, for that matter) that letting a car that's fully-charged sit causes additional degradation.





garsh said:


> You're correct in that nobody has run that particular test. However, Tesla states in several different ways that you should not generally charge to 100%. When a Tesla reaches the desired charge level, it doesn't continuously trickle-charge - it waits until the charge has dropped 2-3% before boosting it back up. So it would seem that Tesla is saying that charging to 100% - even if leaving immediately after reaching 100% - is not particularly good for battery health.


I think I wasn't sufficiently clear. I absolutely agree that routinely charging to 100% is not recommended. 

What I'm saying is that letting it sit after it's charged to 100% (but not continue to "top off") is no worse than driving it after it's charged to 100%. It's the charging it to 100% in the first place that causes whatever degradation occurs, not it sitting around at that charge. Of course, if you keep allowing the car to "top off" then that amounts to repeatedly charging to 100%, which is worse than charging it one time to 100%.

To summarize, from worst to best:

Continuing to try to charge a lithium battery at 100% (Teslas won't do this)

is worse than

Repeatedly charging a battery to 100% (which can be done by leaving a Tesla plugged in with instructions to charge; it drops a few percent then goes back to 100%; drops a few percent then back to 100%; over and over)

is worse than

Charging once to 100%, whether you drive it right away or let it sit for a month

is worse than

Not charging to 100%


----------



## Ed Woodrick (May 26, 2018)

Harriscott said:


> It appears that staying near 50% is good, smaller SOC swings are better, and L1/L2 charging is better. E.g. you should never supercharge, not even once


Interesting statement since the majority of cars with the most miles tend to ONLY Supercharge their batteries.


----------

