When to charge your iPhone or iPad

Question

Level 10

229,510 points

When to charge your iPhone or iPad

There's a lot of myth and folklore surrounding charging iOS devices (or actually any device that uses Lithium technology batteries). A lot of it comes from the advice given for older technologies, such as Nickel-Cadmium or Nickel-Metal-Hydride batteries. None of this applies to Lithium, however, and some of what we "know" from the NiCd and NiMH days is actually harmful to modern battery technology.

Things to understand:

The "charger" for an iOS device is built into the device. It is not the thingy that plugs into the wall, and it is not the cable that connects the thingy that plugs into the wall to the phone. They are just a source of current and a way to get it to the phone, respectively.
Completely draining a Lithium battery, even once, will kill it. (Unlike NiCd and NiMH, which people really would drain completely to prevent "memory effect").
The internal charger is "smart" - It will prevent the device from being overcharged, and it will attempt to prevent the device from totally draining the battery by shutting down the device before the battery is fully depleted.
When the phone shuts off at 0% it really isn't zero; there's still sufficient charge on the device to prevent the battery from going completely flat. Likewise, 100% is not the maximum the battery can store; it stops charging slightly short of maximum to prevent overcharging.
The worst thing you can do is drain the battery to 0%, then not charge it immediately. After it reaches zero and shuts off there's a small amount of energy left, but if you leave it uncharged for long it WILL go flat and kill the battery. So if it reaches zero, charge it soon (within hours). And never leave a phone unused for weeks or months on end without periodically recharging it.
You should only use high quality USB power sources to charge your iOS device. They don't have to be Apple's (although Apple makes good ones), but they should never be cheapo USB sources, both because they may damage the phone and they may even injure you.
The power source needs to supply at least 1 amp to charge an iPhone, and 2 amps to charge an iPad. Note, however that a power source that can supply more than these values is OK to use; the internal battery charger will take only what it needs. So, for example, you can safely charge your iPhone with an iPad USB adapter.
iOS devices fast charge until they reach about 75%; the rate then slows down to prevent overcharging. So it will reach 75% very quickly (under an hour), but it can take a couple of hours more to reach full charge.

So what are the "rules" for charging? The most basic one is charge whenever you want to, for a long as you want to. There's no reason to let the device drain completely before charging (in fact, it's a bad idea to do that on a regular basis), and there's no need to wait until it reaches 100% before removing it from the power source. You can charge when it's at 40% and disconnect when it reaches 80%, or any other values, without hurting the phone.

The Best Practice, however, is to charge the phone overnight, every night. As it stops automatically at 100% you can't overcharge it doing this. You thus start the day with a fully charged phone. And, if you configure the phone for automatic backup using iTunes or iCloud, the phone will back up every night when it has a WiFi connection and is asleep.

iPhone 6, iOS 9.2.1, 128 GB

Posted on Mar 26, 2016 11:09 AM

Reply

Answer 1

Top-ranking reply

Lawrence Finch Author

Level 10

229,510 points

Jan 19, 2018 11:22 PM in response to navy001

That’s not what I said. My advice is, and has always been, to not worry about when or how long to charge it. Charge when convenient for as long as convenient. Which is also Apple‘s advice. There are several advantages to charging overnight: the battery will be full at the start of the day; if you turn on iCloud Backups it will back up overnight; it will reduce the total number of charge cycles because background processes will use mains power instead of battery power. The last is important because battery life is primarily a function of full charge cycles.

Reply

Answer 2

y_p_w

Level 6

17,762 points

Jan 21, 2018 3:46 PM in response to Lawrence Finch

Lawrence Finch wrote:

That’s not what I said. My advice is, and has always been, to not worry about when or how long to charge it. Charge when convenient for as long as convenient. Which is also Apple‘s advice. There are several advantages to charging overnight: the battery will be full at the start of the day; if you turn on iCloud Backups it will back up overnight; it will reduce the total number of charge cycles because background processes will use mains power instead of battery power. The last is important because battery life is primarily a function of full charge cycles.

Just as an aside, a lot of what you say is sound advice for the majority of users. However, Apple doesn't enable a particularly extreme method for that I've heard used in other battery-powered devices. My parents got a notebook computer that had an "optimized life" battery management setting. This setting would only allow the charge to get to 50% and it would only start charging if the charge level was under 40%. If it was disconnected at 45%, it wouldn't charge until it dropped below 40%. Under such conditions the ultimate life can be orders of magnitude longer if the intent is to only use it on battery for short periods.

Tesla cars have extremely flexible user configurable battery management. Some experts recommend certain settings that could mean the battery will never need replacement, but of course Apple doesn't allow the user to select individual battery management profiles. The average phone user values capacity over longevity - especially in a device that's probably replaced in a few years.

https://electrek.co/2017/09/01/tesla-battery-expert-recommends-daily-battery-pac k-charging/

Therefore, they are already doing well and could last for years and hundred of thousand of miles, but there are also things that you can do to optimize the results.

One of those things is not charging to a full charge too often. Repeated full charges can negatively impact li-ion battery cells, which is why Tesla recommends to only daily charge to 90% capacity and to charge to 100% only when needed for long trips.

** ** **

But if someone wants to really push the optimisation to its limit, Dahn suggests going even lower.

A Model X owner on TMC aims to keep his all-electric SUV for up to 20 years and he decided to reach to Dahn for advice on daily charging to optimize the battery pack longevity. The researcher responded:

“I would recommend charging to 70% normally. When you need a long trip, charge to 100%.”

That’s even lower, but again, it’s still over 150 miles of range on most versions of Tesla’s vehicles and if the need arises, they can actually charge to 100%.

It’s quite easy to set up the charge limit, which can be done in the car or through Tesla’s mobile app. The problem is for unplanned use of the car, it can be useful to have the extra charge.

Reply

Answer 3

Lawrence Finch Author

Level 10

229,510 points

Feb 7, 2018 7:56 AM in response to hasangundogdu

Draining to zero is not a complete discharge; Apple designed it to display zero and shut down before the battery is fully depleted. So as long as you charge it soon after reaching zero no harm has been done. ("Soon" means within a few days). From what you describe you didn't do any harm to the battery. However, there is no reason to discharge it to zero intentionally; if it happens by accident just charge it, but do not go out of your way to discharge it to zero.

Reply

Answer 4

Lawrence Finch Author

Level 10

229,510 points

Feb 9, 2018 2:05 PM in response to FarazSidd

FarazSidd wrote:

Heyy sir Can you please help me

I want to know can we charge our iPhone thrice a day? Will it harm my battery in long term?

If I maintain my battery from 50% - 80% then I need to charge it twice to thrice a day

If this is harmful

Then I need to charge my battery to 100% and then use it till 10% this will work in 1 charge whole day

Tell me which one is good for battery performance and health for longer use?

It will not harm your battery to charge it twice a day, or as many times as you need to. There is also no reason to maintain it between 50% and 80%. The best approach it to charge it overnight, every night, and enable iCloud backups. The phone will do an automatic backup every night when locked and connected to power and Wi-Fi.

For more info, see: When to charge your iPhone or iPad

Reply

Answer 5

Lawrence Finch Author

Level 10

229,510 points

Feb 10, 2018 7:00 AM in response to FarazSidd

OK, time to read and understand what it says:

"If you want to store your device long term" That means if you are going to put it in a drawer and not use it for months. "Long term" is not one day. And you are not storing it, you are using it pretty constantly. So the excerpt you quoted has nothing to do with a phone that is powered on and in use.

Yes, if you put it in drawer it is important to power it down, with the battery at around 50%. (When iPhones ship from the factory they are charged to around 50%). And 50% is chosen so the battery is in no risk of discharging to zero while in storage. The reason they don't recommend 100% is for complex technical reasons based on battery technology that aren't important here.

Reply

Answer 6

Feb 12, 2018 9:47 AM in response to FarazSidd

This is directly from the Apple support site.

Charge your Apple lithium-ion battery whenever you want. There’s no need to let it discharge 100% before recharging. Apple lithium-ion batteries work in charge cycles. You complete one charge cycle when you’ve used (discharged) an amount that equals 100% of your battery’s capacity — but not necessarily all from one charge. For instance, you might use 75% of your battery’s capacity one day, then recharge it fully overnight. If you use 25% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle. It could take several days to complete a cycle. The capacity of any type of battery will diminish after a certain amount of recharging. With lithium-ion batteries, the capacity diminishes slightly with each complete charge cycle. Apple lithium-ion batteries are designed to hold at least 80% of their original capacity for a high number of charge cycles, which varies depending on the product.

Reply

Answer 7

Lawrence Finch Author

Level 10

229,510 points

Jan 19, 2018 1:54 PM in response to chcn

Thank you for your thoughtful post. I will answer it as best I can.

chcn wrote:

There seems to be plenty of evidence that lithium batteries prefer to live life near the centre of their charge range. Just as leaving them deeply discharged for long is harmful, leaving them fully-charged for a long time is harmful too. See, for example http://batteryuniversity.com/learn/article/**_808b_what_causes_li_ion_to_die; search for the text “Charging to 3.92V/cell appears to provide the best compromise in term of maximum longevity”. I note that 3.92V appears to be around 65% on an iPhone.

Yes, that is true for batteries being stored; even Apple says to leave a device to be stored at around 50%. But when a battery is continually being used it isn't the same thing as storage, and an iPhone battery usually cycles over a wide range of SoC. I do keep the 2 iPod Classics that I don't use regularly at around 50%, but the one that I use all the time I leave plugged in all the time and it is close to 10 years old on the original battery.

chcn wrote:

I have experienced this effect with lithium laptop batteris too: keeping it plugged in all the time kills the battery within months. Once I got a replacement battery and programmed my ThinkPad to keep the charge level between something like 40% and 60% most of the time, that battery lasted darned-near forever. (Of course I charged it too 100% when I needed to use it in a mobile application. But at my desk, there was no point.)

That has not been my experience. I have a 4 1/2 year old Macbook Pro that I use mostly as a desktop computer with an external display. It is plugged in most of the time. When I do take it traveling, or I unplug it to check the battery condition, it still gets the 10-12 hours of battery life it did when it was new. I also have a 2011 Macbook Air which I leave off and plugged in most of the time, and only turn it on when I travel. It also gets the 3-4 hours of battery life it did when it was new. That's after almost 7 years of use (The MBP is for business travel, the MBA for personal when all I need is a web browser and email). Back when I had a thinkpad its battery didn't do nearly was well; I think it's more a matter of how "smart" the battery management in the computer is. Apple's batteries are not user serviceable or replaceable, so they have to get it right. So my batteries appear to last darned-near forever, even though they are charged continuously.

On your other points and questions, I have never had an iOS device battery degrade during the useful life of the device, even with charging overnight every night. I consider useful life to be about 2 years. The one exception is my wife's hand-me-down iPhone 4s, which is now at 59% capacity. I will be changing the battery this weekend. The phone is an in-warranty replacement (the power switch broke) and is currently 5 years old. The battery is shown signs of high internal resistance (the battery shows, for example, 20% but jumps to 60% immediately if connected to a charger). I think Lithium technology has come a long way in 10 years. Back when the iPhone first came out Apple recommended discharging until it shut off, then charging to 100% about once a month. They dropped that recommendation about 5 years ago.

Consider also the Tesla, which is entirely powered by Lithium Ion batteries; there have been no history of battery failures reported. Or my 2012 Plug-in Prius. It's battery capacity has not changed in the almost 6 years I have had it, and I tend to keep it near full charge when idle.

To your point about keeping a battery midrange, I also have a 2003 Prius. It's battery is NiMH, and the charge management keeps it between 20% and 80%. The battery still has its original capacity after 15 years and 100,000 miles. But that is a completely different technology.

Reply

Answer 8

Feb 9, 2018 9:59 AM in response to FarazSidd

I don’t understand why people don’t get it, the phone has a built in charging circuit that will not let it over charge, just charge it when ever you want for as long as you want but try not to let it drop to 0

Reply

Answer 9

Feb 11, 2018 9:36 PM in response to Lawrence Finch

Okay I understood we can charge as many times a day it will not make our battery worse

Reply

Answer 10

Lawrence Finch Author

Level 10

229,510 points

Jan 19, 2018 7:30 PM in response to navy001

No, that was to recalibrate the battery gauge, it had nothing to do with the battery itself. It is no longer recommended by Apple. It isn’t harmful, but it doesn’t do any good either. I’m sure you can find sites with all sorts of advice if you look hard enough. That doesn’t make them right. That advice was appropriate for battery technologies from 20 years ago, but some myths die hard.

Reply

Answer 11

Feb 15, 2018 11:02 PM in response to Lawrence Finch

SO we can plug our iPhone to charge at any percent ?

1% 2% or 10% ?

Reply

Answer 12

Lawrence Finch Author

Level 10

229,510 points

Dec 11, 2017 7:10 AM in response to Grriz86

Whatever you read was wrong. See my post above. The best strategy is to charge the phone whenever convenient, ignoring any advice such as you "read somewhere". The very best strategy is to charge the phone overnight, every night. No need to remove it from the power source, as the phone stops charging on its own when it reaches full charge.

Reply

Answer 13

y_p_w

Level 6

17,762 points

Jan 21, 2018 5:08 PM in response to Lawrence Finch

Lawrence Finch wrote:

Consider also the Tesla, which is entirely powered by Lithium Ion batteries; there have been no history of battery failures reported. Or my 2012 Plug-in Prius. It's battery capacity has not changed in the almost 6 years I have had it, and I tend to keep it near full charge when idle.

There are reports of catastrophic battery failure in Teslas, but they were attributed to a glitch in the battery management that allowed a deep discharge. However, even Tesla recommends that most owners set up their batteries to charge to 80-90% to improve ultimate battery life. There are some interesting discussions on this on Tesla's own user message board.

Charging recommendations. | Tesla

Of course most iPhone users aren't going to keep their devices for 10 years. I can imagine someone trying to keep a Tesla going for 15 years or longer. I've even seen a second generation Prius still working, and that's how old? I heard that owners have a name for the charge range that avoids extremes to exponentially extend the life - the "sweet spot". I've heard of Prius taxis that easily went 400,000 miles on the original batteries. But of course that's NiMH, but research does seem to indicate that reducing the ultimate charge level will result in Li rechargeable batteries lasting considerably longer.

Reply

Answer 14

Lawrence Finch Author

Level 10

229,510 points

Feb 17, 2018 6:43 AM in response to takith

It won’t hurt to fast charge it. It doesn’t heat enough to hurt the battery, and it only fast charges up to 50%, then slows to a more normal charge rate. And at 80% it starts to taper to an even slower charge, stopping completely at 100%.

Reply

Answer 15

Grriz86

Level 1

10 points

Dec 11, 2017 1:31 AM in response to BORg529

I read somewhere that best strategy is to recharge when it is around 20% and leave it plugged in until at least 95%.

In fact, I used to have an iPad that, being lazy, I recharged often when at 2% or even less, i.e. when I had no other option than to plug it in, and very often I plugged it off when it was not even at 70%. The battery lost 10% capacity in less than 100 cycles...

Reply