40-80 rule - Apple Community (2024)

y_p_w

17,648 points

Lawrence Finch wrote:

Regarding Lenovo, they are trying to cover up for their poor design. The link was posted 8 years ago, when they were still using NiMH batteries, which made sense back then.

Lenovo hasn't used NiMH batteries in decades. I was issued a T61 (circa 2007) for a contract job back in 2011, and that definitely had an Li-ion battery. But I do have a ThinkPad X1 Carbon purchased in 2019, and all those settings are still there. Also - I've been reading that Windows 11 specifically has a universal battery management settings for all devices. Some of their recommendations are a bit weird though. I certainly wouldn't recommend having to "exercise" a battery. But they do recommend using some sort of "smart charging" setting for devices plugged in most of the time.

https://support.microsoft.com/en-us/windows/caring-for-your-battery-in-windows-2db3e37f-5e7d-488e-9086-ed15320519e4

Like all batteries, lithium-ion cells age and deteriorate over time and with use. To help extend battery life and performance, try to keep the battery level between 20% and 80% several times a week instead of using your device for only a short amount of time, and then plugging it in to recharge the battery. If your device supports Smart charging, turn it on to make sure that your device stays charged to the recommended battery level—even if you keep your device plugged in.

But again, there is a ton of research that shows that Li-ion batteries can last longer as long as they reduce their charge range, and there are many non-Apple battery management systems that can be programmed to do that. The closer one gets to the maximum and minimum charge range will result in greater degradation. I don't see why that's so controversial to you. There are tons of research papers on how reducing depth of discharge and limiting state of charge increases overall battery longevity.

And there's no particular reason why Apple has a 500 cycle rating for iPhone batteries, but 1000 cycle ratings for their large devices - other than they can avoid charging to slightly higher levels and discharging to slightly higher levels with their larger batteries. I noticed that you do understand that 0% and 100% are "chosen" points. They can be moved. And it's pretty obvious that Apple choses to use a lower charge range in battery powered devices larger than an iPhone.

But in the end I usually recommend not worrying about it and just allow Apple's battery management to do its thing. Keeping it simple has worked pretty well for Apple. And it's only $49/69 to replace the battery, so it's not a huge cost. However, I think there's a lot about battery longevity that Apple doesn't explain in order to keep things simple.

Lawrence Finch

203,748 points

y_p_w wrote:

I'm really just approaching this from a theoretical standpoint. An automated system that places a floor and ceiling to the charge levels would be ideal, but so far Apple has chosen not to allow that like how other battery systems can be customized to sacrifice run time for battery longevity.

Apple has done EXACTLY that with Optimized Charging. It places a ceiling of 80% IF you follow their advice and charge overnight. And there is a “floor” of 20%, at which point the phone goes into low power mode. The 40-80 “rule” is folk wisdom with absolutely no basis in reality. Your theoretical standpoint is a flawed theory; there is no basis in reality for it. And apparently you either didn’t read or didn’t understand my previous post.

The phone charges to 80%, then stops. All energy use after that comes from the power source, not the battery, so it doesn’t use up the battery capacity. It resumes to reach 100% when you start using the phone, which will start it decreasing immediately. The actual FACTS of Lithium chemistry batteries are:

• They should not be left at 100% for long periods of time. That doesn’t mean that they should never be charged to 100%, only that they shouldn’t be left there. If you plan to take your Tesla on a long trip they tell you to charge it to 100%, but in normal driving it stops at 80%.
• They should not be discharged to zero and left there. Apple deals with that 2 ways; first, the warning at 20% and switch to low power mode, and then if you do accidentally discharge it to zero, it shuts off. But zero is not zero; there is some reserve, as you will see if you try to turn it on; you will get a low battery warning, so there is still enough energy left in the battery to display that warning.
• The warning at 20% is not to prevent it from going below 20%, which actually will do no harm; it’s to tell the user that it is in danger of going to zero and shutting off in the middle of something important.

There is absolutely no theoretical or actual reason to keep the battery between 40% and 80%. That was a guideline for Nickel-Metal-Hydride batteries such as the older Toyota Prius uses, not Lithium ion. And yes, if you have a Prius (I do) it really does keep it between 40% and 80%. My Prius is 18 years old with 120,000 miles and the original battery, so it clearly works for NiMH. My newer plug in Prius charges to 100% when running on battery power alone, but in hybrid mode it drops it to 80% and holds it there. In battery only mode it starts the engine and starts charging it at 5%.

Regarding Lenovo, they are trying to cover up for their poor design. The link was posted 8 years ago, when they were still using NiMH batteries, which made sense back then.

y_p_w

17,648 points

I wouldn't say it's necessary. It's a technique that can theoretically allow a battery to last a lot longer. There are quite a few battery charging systems that either keep a charge within the middle of the charge range or at least can be programmed to limit the charge range - like a Tesla car battery management setting to reduce the maximum charge level. I've used a few Lenovo notebook computers that have a "maximum battery longevity" setting or maybe a slider that chooses between best battery life or best performance.

Another way is to oversize a battery and then use less of the range. There's always a little bit of margin at the top and bottom, and that can be played around with to boost longevity. An iPad battery has a rated 1000 cycles, but an iPhone is 500. The technology and suppliers are the same.

But doing it manually is a very difficult task. I don't like hovering over my devices checking the charge level. I get it dropping due to background activities. In the end it's cheap to replace the battery, so I'd rather have the convenience of using my battery powered device. In the end, the battery is supposed to serve you, and not vice versa.

anypats

21,289 points

ChrisJ4203

230,389 points

y_p_w

17,648 points

ChrisJ4203 wrote:

I would not get any work done if I spent that much time obsessing about my battery charge level. I plug my in at night, it gets charged and backs up to iCloud. In the morning I unplug it and start to work. When I get home at night, I still have sufficient charge to last me until bedtime. I consider myself a moderate to heavy user, but I've never not been able to last a day on a charge, and have about 50% battery remaining when I go to bed. For longer days, like you, I can plug into the car and get some charge there, and that little bit is not going to have that big an effect on charge cycles. Between my iPhone, iPad, Apple Watch and MacBook Air, I'd not be able to do anything except monitor charge levels.

It's not so hard if it's automated, but then that runs into the issue that one would be deliberately reducing the useful charge range. That's no so bad if it's a car battery with a rated 300+ mile range being used on a 50 mile round-trip commute. But for a device like a mobile phone it's a little bit difficult to use that way.

I have set up some notebook computers that way. But those are really more "desktop replacements" where they might be used for a few minutes at a time off adapter power.

Lawrence Finch

203,748 points

It’s not only not necessary, it is counterproductive, because it means that the battery is the only thing ever powering the phone, so following it will significantly shorten the useful life of the battery. The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern.If youenable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates.

The advantage of overnight charging is that for several hours every night the battery is not powering the phone; the external power source is. It is meaningless to compare it to other uses; unlike a Tesla, you can use the phone (or it can do its internal tasks) while it is plugged in. Try that with a Tesla! (I”m picturing a 100 mile long extension cord 😏)

y_p_w

17,648 points

Lawrence Finch wrote:

It’s not only not necessary, it is counterproductive, because it means that the battery is the only thing ever powering the phone, so following it will significantly shorten the useful life of the battery. The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern.If youenable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates.

The advantage of overnight charging is that for several hours every night the battery is not powering the phone; the external power source is. It is meaningless to compare it to other uses; unlike a Tesla, you can use the phone (or it can do its internal tasks) while it is plugged in. Try that with a Tesla! (I”m picturing a 100 mile long extension cord 😏)

I'm really just approaching this from a theoretical standpoint. An automated system that places a floor and ceiling to the charge levels would be ideal, but so far Apple has chosen not to allow that like how other battery systems can be customized to sacrifice run time for battery longevity. It's never been a mystery as to why iPads and MacBooks are rated at 1000 cycles while iPhones are rated at 500 cycles. The devices are bigger, the batteries are bigger, and they've opted to use just slightly less of the theoretical charge range. And it's relatively cheap to replace the battery (although in some countries Apple only does a complete swap), so why bother.

I first heard about using only the center of the charge range when it was about hybrid car batteries that have literally lasted the entire life of a car where they're still usable after a half a million miles. Part of it would be that they really don't need it for anything put as an energy sink for the regenerative braking and for supplemental or low-speed power. But another is that when you only need so much of the battery capacity, is it going to be missed when it's lost?

Lenovo has an extremely aggressive battery longevity setting for its notebook computers. It's designed for when one rarely uses the battery alone. The battery is still needed for peak power demands, but it will literally use only 0 to 50% and won't start charging until it's below 40%. But it is extreme. I'm not sure if there's any smartphone that has a similar feature.

https://support.lenovo.com/us/en/solutions/ht078208-how-can-i-increase-battery-life-thinkpad-and-lenovo-vbke-series-notebooks

Battery longevity is affected by age, the number of charge cycles, amount of time at full charge, and high temperature.

For maximum lifespan when rarely using the battery, set Custom charge thresholds to start charging at 40% capacity and stop at 50%, and keep the ThinkPad cool. The thresholds can be adjusted in the Battery Maintenance settings of Lenovo Power Manager.

If the battery is used somewhat frequently, set the start threshold at around 85% and stop at 90%. This will still give a good lifespan benefit over keeping the battery charged to 100%.

But possibly the best way to maximize the battery longevity is to use a charging case or always connected to power (like a USB power pack). But that would just transfer the battery wear to the power pack. I have't paid too much attention to it recently, but when Amtrak went to using phones as ticket scanners and overall passenger management devices, they used a special case that included a barcode scanner and battery. Even though the internal device was an iPhone 4S with a rated 200 cycle longevity, they were being used every day for years without needing "battery replacement".

muguy

76,681 points

No. Settings > Battery > Battery Health Turn on optimized battery charging.

Use your phone as you normally would. Best practice is to charge overnight.

Nothing else to do.