When to charge your iPhone or iPad

I have been an Electrical/Electronic Engineer for 50 years. I am a life member of IEEE. My projects included the first electronic landing system for aircraft carriers; first deployed in 1970, the same system is still in use on 10 Nimitz class carriers. It was also adapted by NASA as the landing system for the space shuttle. Regarding Lithium technology batteries, that's easy; there are published standards on the technology from manufacturers of both the batteries and the charging technologies for them. I read and follow them. Specifically for Apple products, Apple has published recommendations for use of batteries in Apple products. Most of what I post comes from Apple's recommendations. I have also measured charging curves for different models iPhones and iPads, which is where I got information on charging times that is not published by Apple.

markfromsolanabeach wrote:

I vaguely remember an old Apple Support Article which, at one point in the history of iPhones and iPads, explained that there was a Finite Number of Charges allocated to the aforementioned products. For instance, regardless of what percentage your product has left, i.e. 10%, 50%, 80%, it was documented that a User could plug in to Charge your iPhone and iPad, "x" number of times, which if I recall correctly was around 500 charges, before the Battery would need to be replaced. As an aside, do you know, or understand, why Apple made the choice of not allowing easy access to the Battery and also went from having External SIM Cards to inaccessible Internal SIM Cards?

The battery in a current model iPhone is rated at 600 full cycle charges to 80% battery capacity. There is also an age limit of about 5 years, but most phones will reach the charge cycles first. A "full charge cycle" means from 100% to zero, and recharge to 100%. But if you charge the phone at 75% that is only 1/4 of a charge cycle; if you did this 4 times it would count as one full charge cycle. So it has nothing to do with the number of times you plug it in. To follow this example, if you always charged it at 75% you could plug it in 2,400 times. And even then you would still have 80% of the battery capacity. For most people they will replace the phone before their battery drops to 80% capacity.

To make a battery that was replaceable would make the phone twice the thickness that it is. As most people will never reach the point of replacing, doubling the thickness (and weight) of the phone would make the phone less desirable. And Apple will replace the battery, for the few users that need a new battery, for $79. A good quality replacement battery will cost around $40, so the cost savings for a replaceable battery is only $39.

All iPhones have replaceable SIM cards; there has never been any iPhone with an inaccessible Internal SIM Card. I don't know why you think they are not removeable; do you actually have an iPhone? See: iPhone and iPad: How to remove the SIM card

Are you aware of any similar sounding Support Articles to which I am referring, and if so, do you agree with the Logic I described above, as it pertains to supporting a Finite number of Charges? In Concept, being that Lithium-Ion Batteries are currently the most efficient and effective choice for charging devices, Applied Science should determine the most optimum means for Efficiency and Effectiveness, as it relates to charging and discharging of lithium-ion batteries. Are you aware of any Scientific evidence that can be applied to support this discussion?

Lithium chemistry batteries (every one of them, regardless of manufacturer) as well as all other secondary (rechargeable) batteries have a finite life. I'm sure you can find lots of useful information with Google. One starting point: http://www.buchmann.ca/buchmann/ Here are a couple of Apple articles listed: Batteries - Why Lithium-ion? - Apple

In my own humble opinion, I believe this was likely just a Legal Disclaimer from Apple regarding the product's Battery Life Expectancy, as a means of setting User Expectations, much like when the car manufacturer, Tesla, originally stated that the Life Expectancy for the S Model lithium-ion battery to be somewhere around 80,000 miles, which was later proven to be more like 100,000 miles. In both cases, a means of setting user expectations, taken from Sales, Underpromise and Overdeliver.

As with Tesla, batteries that Apple uses have a certain lifespan rating. Some batteries will last longer, others will last less time. These result from minor variations in manufacturing techniques, operating conditions, luck, and also how long they are in use. For example, batteries that are used near the upper end of their temperature ratings won't last as long as batteries kept near the middle of the range. And if you routinely drain them to zero and let them sit before recharging them this will significantly shorten their life. And imagine if Tesla said the battery was good for 100,000 miles, and someone needed to replace it at 99,000 miles. Some people would sue Tesla. Rating it at 80,000 miles takes into consideration all of the variables I mentioned. In addition, for Tesla, unlike Apple, measuring miles is only an indirect measure of battery life. The actual life is number of full charge cycles. If someone does all of their driving at 100 MPH they will clearly go further for the number of full charge cycles than someone who drives 60 MPH. So Tesla had to take this into consideration in estimating miles, even though the actual battery life is determined by full charge cycles, not miles.

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

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.

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/bu_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.

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.

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.