iPhone's 80% Charge Cap Barely Boosts Battery Life, Year-Long Test Reveals (macrumors.com) 79
A year-long test of Apple's 80% charge limit feature on the iPhone 15 Pro Max has revealed only marginal benefits to battery health. MacRumors editor Juli Clover reported her device maintained 94% battery capacity after 299 charge cycles, compared to 87-90% capacity for iPhones without the limit. The opt-in setting, introduced with iPhone 15 models, aims to extend battery longevity by restricting maximum charge.
Clover adhered strictly to the 80% limit for 12 months, noting occasional inconveniences like depleted batteries during long days. While the test showed slightly better battery health retention, Clover questioned whether the trade-off in daily usability was worthwhile. She adds: I don't have a lot of data points for comparison, but it does seem that limiting the charge to 80 percent kept my maximum battery capacity higher than what my co-workers are seeing, but there isn't a major difference. I have four percent more battery at 28 more cycles, and I'm not sure suffering through an 80 percent battery limit for 12 months was ultimately worth it. It's possible that the real gains from an 80 percent limit will come in two or three years rather than a single year, and I'll keep it limited to 80 percent to see the longer term impact.
Clover adhered strictly to the 80% limit for 12 months, noting occasional inconveniences like depleted batteries during long days. While the test showed slightly better battery health retention, Clover questioned whether the trade-off in daily usability was worthwhile. She adds: I don't have a lot of data points for comparison, but it does seem that limiting the charge to 80 percent kept my maximum battery capacity higher than what my co-workers are seeing, but there isn't a major difference. I have four percent more battery at 28 more cycles, and I'm not sure suffering through an 80 percent battery limit for 12 months was ultimately worth it. It's possible that the real gains from an 80 percent limit will come in two or three years rather than a single year, and I'll keep it limited to 80 percent to see the longer term impact.
Stop using the phone that much (Score:2)
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Yeah same here (Score:1)
Re:Yeah same here (Score:4, Interesting)
The difference will be a lot more after two or three years.
It's like compound interest. Tiny differences really add up over time.
Re: Yeah same here (Score:2)
My 15 Pro Max is coming up on a year old. Max battery capacity is 99%. I rarely see it before 50% in a day, even with 80% charging.
Re: Yeah same here (Score:2)
So if I only use 80% of my battery, it will have 5% more capacity a year later?
5% more capacity that I wonâ(TM)t use.
Makes no sense.
Seems pretty good actually (Score:5, Informative)
I upgrade my phones ... rarely. I still have an iPhone Xs Max that I purchased at release time so many many years later I'm happy that the original battery still gets me through the day (I'm not hooked to my phone screen all day).
So if after 12 months they saved 4 to 7% of the capacity, that's big 5y later.
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I kept my previous iPhone for over 5 years, it had 79% of original battery capacity left when I retired it.
I figured I'd try the 80% charge thing on my 15 Pro Max and turn it off if I run out of battery because going by previous experience the battery will probably last pretty long anyway. Haven't had any issues with running out of juice so any savings at all are worth it to me I guess.
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I read somewhere (can't find it now) a research showing the capacity loss is not linear through batteries lifespan. They actually lose more in the first year and then a little less in the upcoming years.
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Maybe we should measure battery life in Dog Years.
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This is correct, and the benefit being reported is actually quite significant. The problem here is ignorance and expectation.
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It's actually kinda crap though. My Pixel 8 Pro is a year old and still has in excess of 100% of the rated battery capacity left. I charge it to 75% and discharge it to no lower than 35% most of the time, although for a month I was charging it to 100% daily.
Apple seems to have long term issues with battery degradation, going back to the iPhone 6 at least.
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So if after 12 months they saved 4 to 7% of the capacity, that's big 5y later.
That's actually not how battery degradation works. For the most part a capacity degradation initially drops to somewhere around 85-90% and then stays there FOR A LONG TIME, before dropping off the cliff. There is no conclusion you can draw at all about those 4-7% after one year, that would apply 5 years later. The degradation isn't linear. It's not losing 7% per year.
Exactly (Score:5, Insightful)
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I agree. Even just looking at the numbers, degradation was more than halved. And actually, the first 5% go quickly, after that the degradation settles down, so it may be more than halved. Seems like it works as intended.
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Typically battery lifespan ratings are given as the number of cycles until the battery reaches 80% of nominal capacity. Extending lifespan can be done in three ways:
- Underrate the nominal capacity so that it starts at say 105%, meaning it can lose 25% instead of 20% before EOL. This can be combined with limiting charging to 100%, not 105%, i.e. about 95% of the battery's true capacity.
- Alter the chemistry to survive more cycles before reaching 80% of nominal capacity.
- Reduce stress on the battery by char
Re:Exactly (Score:4, Insightful)
Someone who's bad at statistics is writing articles. This "tiny difference" is huge. And waiting another year would give a lot higher quality information.
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And waiting another year would give a lot higher quality information.
I agree. The first year is interesting, but the 2nd, 3rd, and 4th years would be even more interesting. We don't know if the degradation accelerates, decelerates, or maintains the same speed.
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~20% additional degradation after 4 years of use is still significant
Except that's not how it works. Battery degradation isn't linear over time. There's an initial drop and then stability for most of the rest of battery lifetime. You don't loos x% every year. You loose x% early on, and then it stays there for years when suddenly you notice the phone really REALLY struggling to keep charge over the day.
You can draw no conclusion about TFS. It was some dude playing with data without understanding it.
Seems very testable in the lab (Score:2)
So the question is, did Apple release this without real testing? Or did they test it, and decide that the small improvement was still worth shortening time between charges by 20%?
Incidentally, my Moto G goes for 3 days between charges, so I'd bet reducing the power consumption of the phone would go a lot farther towards increasing battery life, than reducing how much you can charge it.
Re: Seems very testable in the lab (Score:2)
My moto g power 2021 still goes 4-5 days on a charge and I surf on it during lunch and breaks like I'm doing right now.
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Yeah mine is the same year. But I use GPS a lot, and that sucks the battery a lot faster than web surfing. Still, I'm pretty happy with it.
Re:Seems very testable in the lab (Score:5, Insightful)
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I can see that. For us Moto G users, 299 charge cycles spans about 3 years, so not as significant.
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Not really. Degradation isn't linear. The person playing around is very likely going to find that next year both his phones are in the 10-13%. It's a pointless mix of very unscientific bullshit in TFS.
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I suspect apple didn't do anything. Instead someone there just read a few papers by Zsoldos after noticing a lot of phone makers, laptop makers and EV makers adding 80% maximum charge option to their hardware, and then decided to follow other manufacturers in applying best practices as outlined in those papers.
Max charge is half the story... Max discharge... (Score:5, Informative)
Limit Max discharge... (Score:2)
... The key to maximizing battery life is to stay in the sweet spot, not fully draining, and not fully charging. These statistics are a lot better than some random anecdotes: https://batteryuniversity.com/... [batteryuniversity.com]
Not fully draining is pretty easy to do on any Android. I just set my "Battery Saver" to kick on at 40%.
The little auto-notification, and slight reductions in performance are annoying enough to remind me to go drop it on the charger for a bit. Obviously if you avoid using the top 10-20% and the bottom 40% of your charge you only get 50-60% of rated capacity, but I just way overbuy on mAh by x2 and don't have a problem going a full day or more between charges for four or five years. Can IOS do something s
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You really can't fully drain a lithium battery any more, unless it's some weird boutique battery manufacturer who still makes controllers that let you do that.
Most controllers will shut the battery off around 3-5% mark. The main reason why you may hit full empty by accident with those is badly miscalibrated charge assessment by the controller. Which is actually something you can cause to a lifepo battery if you spend a long time without charging it to full, because that's how controller calibrates itself.
Re:Max charge is half the story... Max discharge.. (Score:4, Insightful)
And therein lies the issue with the article.
The guy says he's on his phone pretty much all the time - he's complained having 80% meant it runs out on him all the time.
To me, if you're getting that the 80% limit isn't going to benefit you as much as it would someone who basically manages to make their phone last a day and a half or more - their phone rarely goes below 50% when they're done with the day,
For such light users, the max 80% might have greater effect on battery longevity because it's always staying at a high state of charge.
My phone (iPhone XS Max) I got on launch day. It's basically been lightly used as I rarely do heavy things with it to drain the battery - it rarely goes lower than 60% when I'm done with it. It's right now at 90% capacity. I'm sure it could be higher if I had the 80% option.
If you aren't draining the battery already and still have plenty of charge on your phone, you probably will benefit from the 80% option. If you're someone where you need to charge it by noon, the 80% option isn't going to do as much.
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Also not charging at 27W. It's a shame that few phones let you limit the charging speed.
Keep old 1A, or even better 500mA, chargers around and use them for your daily charging needs. Computer USB A ports (with a data blocker) are good too, but beware of USB C as some offer quite a bit of power.
Use high power charging for emergencies only.
What did they expect - 110%? (Score:5, Insightful)
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Well, maybe, yeah. Some manufacturers give the nominal capacity of their battery as much lower than the true capacity.
Korean EVs are a great example of that. 4-5 year old Kias and Hyundais with 64kWh battery packs typically still have 100% capacity remaining, because their true capacity is more like 70kWh. The extra 6kWh is unusable, the car won't let you charge that high, or discharge too low. Any degradation so far is within that "buffer", and it's probably quite low anyway since you are effectively charg
What I'm reading here is... (Score:5, Insightful)
...that this setting halves decay.
How is that marginal?
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Much more than halves. The increase is exponential, and last twenty percent or so where it really starts to feel.
Charging 20-80% ten times is likely going to lead to less capacity loss than charging once from 80% to 100% (additional factors being battery temperature, its current age aka how much it already degraded and specifics of chemistry involved, some tolerate charging at top end better than others).
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...that this setting halves decay.
How is that marginal?
Battery decay isn't linear. Going down to 80% in one year vs 90% doesn't mean one battery will last twice as long as the other, it means that at the end of the second year you'll likely find one battery at 76% and the other at 78%. Battery decay drops quickly over life to around 85% and then sort of hovers around that 80-90% mark for a really really long time.
Not really any surprise.... (Score:4, Interesting)
All Apple did here was follow the generic advice from the supposed experts in battery chemistry who keep reiterating that your lithium ion type batteries will last longer if you don't charge them over 80% of their capacity (vs 90% or worse yet, 100%).
The other half of that is that it's not good for them to drop below a 40% charge either. In a perfect world, they like to optimally stay between a 40% to 60% charge.
Obviously, that's not incredibly useful in the real world, though -- so what we wind up with are batteries designed big enough so some degradation of the original capacity isn't considered an issue, plus a realization that except for the real extremes (discharged to nearly empty or charged all the way up and kept at a full charge for a length of time), the extra degradation is relatively minimal.
With your typical phone batteries, they're cheap enough so most people are fine with the idea they'll keep charging up well enough to give you hours of usage at a time for at least 2 or 3 years. Then you just replace them. When you've scaled this up so far, you're talking about multi-thousand dollar battery packs in electric cars? You're also looking at a situation where they get managed more actively by more complex monitoring/charging software, probably get actively climate-controlled, etc. So they're designed to have a much longer lifespan. But the same general thing applies. Charge them daily to 80% instead of 90% and you might get another year of decent life/use out of them? But you're talking about, say, 12 years instead of 11, or 11 instead of 10. Most vehicles owners don't care because they won't even keep their vehicle that long before trading it in, or they bought a used one where they don't have a way to even know the charging history the previous owner stuck with. So the typical advice is just to use it whichever way meets your needs best.
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When you've scaled this up so far, you're talking about multi-thousand dollar battery packs in electric cars? You're also looking at a situation where they get managed more actively by more complex monitoring/charging software, probably get actively climate-controlled, etc.
What maximizing the battery's lifespan mostly comes down to is having significantly more capacity than you typically need, even with EVs. The earlier Nissan Leafs actually did experience some pretty serious degradation because, in addition to not having active thermal management, even the average commute would end up putting nearly a full cycle on the battery every workday.
Same deal with cordless lawn tool batteries. They'll last significantly longer if you buy several of them and swap 'em out as soon as
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Leafs still have that horrendous battery degradation. They just ship with more overprovisioned batteries now, so you don't see it happen until a bit later.
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Keep in mind that this is in addition to changes all manufacturers have already made. The constant trickle to keep the charge at exactly 100% while it's sitting on the charger for hours. I would say even automatic battery saver modes do more than keep the phone from shutting off. If you make it to the end of the day with a charge above 10% (or better yet 15 or 20) when you charge it, you're doing a lot for the health over letting it run flat and charging it.
Software 'bug' (Score:3)
Note: I have and like my iPhone XS. But...
Sounds like reported battery life, at least on an iPhone, is "buggy".
I fully realize that the charged capacity is arbitrary - it's a cutoff, based on voltage calculations. They arbitrarily say "this is 100%" or "this is 90%". The solution to this isn't to "charge to 80%", it's to provide 20% more battery to the phones and charge to 100%, then consider everything -above- that "over charging" (and represent it as such - eg. 120%). Likewise, if the battery decayed to 99% or 97% or what have you (as a percentage of the threshold considered "fully charged"), it should simply report it as that percentage instead of lying and saying it's still getting the same percentage of charge.
This would be a much appreciated functionality for those of us who understand how batteries work. It's not like storage or a bucket, which you can "fill up" physically.
Personally, I purchased a 'battery case' for my phone and haven't been happier. I'm no longer worried about having to charge with an external battery pack on a long day of travel, and I no longer need to worry about the external battery pack. I don't really look at battery capacity anymore, it's usually somewhere between 80%-100% when I wake up and if I notice it's getting low, I'll turn the case on and top off to about 80%. I was able to take a 4-day backpacking trip without any concern for battery life this way (and had the phone off for most of the trip, but still).
4% is barely?! (Score:5, Informative)
I have four percent more battery at 28 more cycles
You are fucking idiot if you qualify this is as barely. That was just one year. Do you you not think the effect will compound? After five years that's going to be a difference of at least 20%!
"but I just buy a new phone every year" said the idiot who "cannot afford" to drive an EV and pollutes endlessly while needlessly generating e-waste.
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That's not how compounding works. With compounding, after five years, you would have 27.6% more capacity.
https://en.wikipedia.org/wiki/... [wikipedia.org]
Check your assumptions and your math (Score:2)
4% less: 0.96^5 = 0.8153726975999999
4% more: 1.04^5 = 1.2166529024000001
I wrote "difference" which doesn't tell you if the answer is more or less but people generally use 100% as the ceiling which is why I went with 4% less. Also, I didn't write 19.5% difference because the rates of degradation are not linear. I assumed that the rates between the two will diverge, thereby amplifying the difference. As a result It seems like a safe assumption to say this would drive it beyond 20% less charge, a difference of
Avoiding the real soloution (Score:4, Interesting)
They COULD try something radical like making changing the battery easier than re-manufacturing the phone. The phone doesn't actually need to be thin enough to chop onions.
Re: Avoiding the real soloution (Score:3)
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This is probably going to be mandated in EU soon. And just like with USB being the universal charge port, it's likely going to propagate world wide from there.
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It's really not that hard to change the battery in an iPhone -- especially when you factor in that it's something you should only need to do once every 3-5 years. I'm on year 4 for my SE-2 and will probably change the battery next year. Anyone who say they have to buy a whole new phone because changing a battery is too hard or too expensive is.. well.. wrong.
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They COULD try something radical like making changing the battery easier than re-manufacturing the phone. The phone doesn't actually need to be thin enough to chop onions.
I don't know why you think changing an iPhone battery is hard. I mean you can literally walk into the electronics store in your local supermarket, throw down a $40 and your battery is magically changed.
Not everything needs to be able to be done by the end user. When was the last time you replaced your own timing belt on your car? Why accept a service industry as appropriate for one device, but not another?
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I've never needed to change a timing belt. But I've always done my own automotive repairs.
Why should changing the battery in a phone be more akin to changing a timing belt than it is to putting in a new air filter?
It's about longer term savings (Score:2)
In my case, I'm on the fourth battery of my Samsung S4, and I began using a battery limiter app during the second one.
The last two batteries had (and still has so far) a longer lifetime than did the first one that actually became bloated after two to three years and the second one, I'd say about 75 to 100%.
That's why a swappable battery was a requirement for my new phone purchase and I had only a few models to choose from nowadays. Not going to renew a phone just for the battery just like buying a new car b
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I was looking for more comparisons of Samsung with Apple, but this is the only mention of Samsung, and not a comparison.
For what it's worth, I think Samsung had an 85% limit. I was using it until they changed the settings in a major upgrade some months ago. Then it became an 80% option, a "smart charging" default option, and a new trickle option that was supposed to flutter between 95% and 100% while plugged in. But there was another major upgrade that seemed to eliminate all options in favor of a new 'supe
299 charge cycles?? Try 700 (Score:2)
I charge my phone every day, and typically give it a boost midway through the day. When traveling I might charge it 2-3 times a day. In one year my phone probably gets charged 400 times, so in three years (about average for me) that's well over 1000 charge cycles. I'm not sure how long most people keep their phones for, but it's probably at least 18 months, unless you're prone to dropping yours.
I don't see the value in testing for less than 370 cycles. 300 cycles is probably the bare minimum the bat
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Welcome to stupid journalism. If they waited until another year passed by someone else would have already published a near useless article. They have to scoop the story before it's ripe just to not seem irrelevant later. By the time they have enough numbers for useful results, everyone has moved on and fewer people will even be reading it.
Stop cycling (Score:2)
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Charge less often? (Score:1)
Instead of charging to 80%, if I end the day >70%, I just don't charge. It's easy enough to charge in the middle of the day if you need to, but with the large battery on my google phone (the 6 pro), and the sipping that OLED screens do nowdays, if I don't use it too much, I finish above 70% on the first day... meaning I often have around 35% at bedtime on the 2nd day. Charge less often.
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I can't be arsed to read the article, but maybe she was only charging when she hit some arbitrary number, like 20% or something.
But, come on, it's 2024. Charge your phone when it needs charging.
Seems like a good result (Score:2)
Old information (Score:4, Informative)
There have been several studies on this subject about half a decade ago. Which have been confirmed several times, most recent being just a few weeks ago for LiFePo chemistry batteries.
The general idea is that lithium batteries have two main failure modes. Loss of lithium inventory and dendrite growth, as well as several minor ones. The main problem for charge potential loss is loss of inventory. Basically when you charge the battery from the factory for the first time, it loses about 10% of its capacity immediately because some of the lithium in the electrolyte gets stuck to the negative pole permanently. Remaining capacity is then marked as nominal on the battery, and it moves in. But as battery is charged, more and more lithium is permanently stuck to that pole, causing continuous permanent loss of maximum capacity as you charge.
However by far the most damaging part of the cycle is 80% to 100%. That is when highest amount of lithium inventory loss occurs, and increase is exponential. So as long as you charge up to around 75-80%, your battery will be able to retain it's lithium inventory for much longer than if you charge all the way to full every time. This is why most modern phones and laptops have an optional charge limiter that will not charge lithium battery beyond 80%.
Overall, if you want to read some of the best papers on the subject, search for "Zsoldos" on google scholar.
just 1 year so far (Score:2)
iPhone's 80% Charge Cap Barely Boosts Battery Life in the first year
It's entirely possible that there will be a bigger benefit at the end of the second or third year. Maybe the year-over-year dropoff will be along the lines of 6%, 12%, 18% instead of 6%, 18%, 36%. If your battery is good enough that an 80% charge gets you through the day, it seems there's no reason not to.
Doesn't limiting the charge just mean... (Score:2)
... you're acting like it's already dying, even when it's still good?
299 times 80% charge means 299 times you told the battery it was "OK to be limited". I'd rather have the actual capacity available.
Personally, I don't kill a battery in a single day. Does charging my iPhone every two days make it last longer? Or should I go three days, when it will actually be low?
(no, I'm not a phone addict)
Nice Feature (Score:2)
From the data provided, this is a useful feature. If you're planning on replacing your phone after two years, it's not worth it, but if you want to keep it 4+ years, it's clearly a good idea. If you're worried about running out of power, get a spare external battery (they're cheap).
WTF? (Score:2)
Like everyone is saying, the headline is wrong, since the actual data in the article makes it obvious what most of us already knew: being gentle(r) with lithium ion batteries than what the manufacturer sets the max/min charge levels to can extend their usable life significantly.
Case in point: back in 2018 I bought three Moto G5 Plus android phones for myself and my family. Two of the three phones are still going strong, one is long dead. The difference? Two of us routinely charged to only 80%(ish) and wer
My iPhone 15 Pro Max's results (Score:3, Informative)
I've had the 80% limit set on my iPhone 15 Pro Max since the day I got it. It's currently showing 140 charge cycles (I dual-wield phones and sometimes switch to an Android device for a week or two for dev stuff), and a max battery capacity of 100%.
This is *much* better than I experienced with my iPhone 13 Pro a few years back. So I can't complain at all. And the 80% limit on my Pro Max leaves me with more than enough battery to get through the day, and then some.
garbage article. (Score:2)
Suffering?? (Score:2)
>"I'm not sure suffering through an 80 percent battery limit for 12 months was ultimately worth it."
I am not a phone addict. I might use 20% charge at most on a typical day on my Samsung A52. Then it is placed on a charger when I get home. It charges to 80% and stops. For all the people like me, and I suspect there are tons, there is no "suffering", it is just a pure bonus to limit the charging. On the very rare occasion I might want to ensure I have FULL capacity (I think I did it once, ever), I ju
What's the right metric? (Score:2)
The real question is whether a user can get through an entire day without charging. It seems like if intentionally limiting battery charge to 80% is acceptable, then the capacity degradation after several years to drop to 80% is also acceptable. If that degradation after several years is not acceptable, then the intentional charging limitation is also not acceptable.
NB (Score:2)
You will still need to charge to 100% from time to time (every 2-4 weeks) to keep the battery calibrated.
If you always charge to 80%, you will eventually start charging more and more due to the inevitable degradation.
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The max voltage you can put into lithium is 4.21v (some variance allowed, but lets go with 4.2)
When your phone tells you "100%" it's just translating "4.2=100"
When you set an 80% cap, it sets the max charge to say, 4.00v. and it won't matter because you'll probably never degrade the battery below 4.00v max charge, and you don't need to go above 4.00v to find out what the max volts still are, as long as you're hitting 4.00v. It'll regis
5% per year is a lot (Score:1)
If they see this kind of difference annually over Apple's expected service life of the device, that will have compounded significantly, by the end of 7 years, the first phone will have ~63% capacity left (which strokes with my experience on battery life), the other will have ~37% left.
That is a HUGE difference, not for the rich that throw away your phone annually, but for most regular people, that is at least years of extra lifetime.
My anecdotal datum. (Score:1)
15 Pro Max, 439 cycles, 89% capacity remaining.
80% limit used for all but 12 days of the past year.
Not charged gently.
Battery health algorithm (Score:2)
The battery health algorithm is secret and software and the OS knows when the 2 year "warranty" is coming up, it's not like you can use a volt meter to calculate it yourself.
My data is much better (Score:2)
iPhone 15 Pro
Model: A2848
Battery health: Normal
Maximum Capacity: 99%
Cycle Count: 254
Manufacture Date: July 2023
First Use: September 2023
Setting the charge limit to 80% has worked out well so far. Unlike the author I have “cheated” a few times and increased the limit to 100% when travelling.
Similarly, my Tesla Model 3 from Jan 2018 with ~65k miles / ~104k km has lost 6% over 6 years with a charge limit of 75% (except road trips).