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Question: Does Plugging an iPhone into Your Mac Affect Battery Life?

I understand that it's a good practice to let your battery go down low before charging it back to 100%. But if you want to transfer pictures does plugging it into you Mac affect the battery life? Say you are at 50% or 75% would plugging it in be harmful? Thanks in advance.

iPhone 6, iOS 8.4, Talking to Siri via "Dashboard"

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No harm whatsoever.

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Mar 10, 2018 1:44 PM in response to MD_Gene In response to MD_Gene

No, it is not good practice to let the battery go low. In fact doing so repeatedly may very likely cause permanent battery damage.


You can charge at any time, for any amount of time.

You can use it while charging.

You can leave it connected to the charging circuit after the battery reaches 100%.

Mar 10, 2018 1:44 PM

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Mar 10, 2018 1:47 PM in response to MD_Gene In response to MD_Gene

MD_Gene wrote:


I understand that it's a good practice to let your battery go down low before charging it back to 100%.

That's false. It's a myth. Charge it as often as you like, for as long as you like, to whatever capacity you like. The only thing that's 'bad' for it is letting it run completely out too many times or letting it drain completely and leaving it sit without being charged for a period of time.

Mar 10, 2018 1:47 PM

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Mar 10, 2018 1:53 PM in response to MD_Gene In response to MD_Gene

MD_Gene wrote:


I understand that it's a good practice to let your battery go down low before charging it back to 100%.

You understand incorrectly. That is a very BAD practice, and it will shorten the life of the battery. that was good advice 20 years ago for Nickel-Cadmium batteries, but it is WRONG for all battery technologies since then (Nickel-Metal-Hydride, Lithium, etc).


See my tip: When to charge your iPhone or iPad

and Apple's Batteries - Why Lithium-ion? - Apple

Mar 10, 2018 1:53 PM

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Mar 11, 2018 5:23 PM in response to MD_Gene In response to MD_Gene

It's good practice to use your battery, but I wouldn't say that it's needed to get it down to 0%. I personally believe it's not necessarily bad to allow an iPhone to reach "0%", but others have a different opinion. 0% is not really an absolute floor. It's a reference point where the battery management system keeps reserve capacity to prevent it from getting into a deep discharge state. If it gets down to "0%" there's still enough capacity left to display an image on the screen asking the user to plug it in. I've allowed my iPhone 7 to go to 0% at least a half dozen times and after over 190 cycles it's still registering about 97% battery health. The important thing to do if it gets to "0%" is to make sure it's recharged quickly.


If anything, using a Mac as the power supply could mean more incoming current which theoretically can create more heat and reduction in battery life. A Mac is capable of of providing 2100 mA to an iPhone, which is more than double that of the standard 5W adapter that comes in the box with most iPhones. I personally don't worry too much about it. I allow my iPhone 7 to charge on my Mac and use the 12W iPad power adapter, where the iPhone will limit intake to 2100 mA. Once it approaches about 80% capacity it will start to back off on the input current regardless of what you're using as a power supply. It does that to protect the battery (and reduce the chance of a battery fire), since it's better to charge at a lower rate once it starts getting closer to 100%.

Mar 11, 2018 5:23 PM

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Mar 11, 2018 5:31 PM in response to y_p_w In response to y_p_w

y_p_w wrote:


It's good practice to use your battery, but I wouldn't say that it's needed to get it down to 0%. I personally believe it's not necessarily bad to allow an iPhone to reach "0%", but others have a different opinion. 0% is not really an absolute floor. It's a reference point where the battery management system keeps reserve capacity to prevent it from getting into a deep discharge state. If it gets down to "0%" there's still enough capacity left to display an image on the screen asking the user to plug it in. I've allowed my iPhone 7 to go to 0% at least a half dozen times and after about 180 cycles it's still registering about 97% battery health. The important thing to do if it gets to "0%" is to make sure it's recharged quickly.



No, it is not good practice to use your battery. It doesn't matter whether or how much you use it. There is ZERO benefit to running it all the way down, or even mostly all the way down.


If anything, using a Mac as the power supply could mean more incoming current which theoretically can create more heat and reduction in battery life. A Mac is capable of of providing 2100 mA to an iPhone, which is more than double that of the standard 5W adapter that comes in the box with most iPhones. I personally don't worry too much about it. I allow my iPhone 7 to charge on my Mac and use the 12W iPad power adapter, where the iPhone will limit intake to 2100 mA. Once it approaches about 80% capacity it will start to back off on the input current regardless of what you're using as a power supply. It does that to protect the battery (and reduce the chance of a battery fire), since it's better to charge at a lower rate once it starts getting closer to 100%.

I'm sorry, but this is absolute nonsense. Actually, a Mac is capable of supplying only 1000 Ma from a USB port, but that's irrelevant. Even if it could supply 2100 Ma it wouldn't matter. You could use a USB supply that could provide 10,000 or 100,000 Ma and it wouldn't matter, because the phone will only use what it needs. The same way the appliances and light bulbs in your house only draw what they need. A typical house has 200 amps of incoming power, but a 60 watt light bulb will only use 0.5 amps.

Mar 11, 2018 5:31 PM

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Mar 11, 2018 5:40 PM in response to Lawrence Finch In response to Lawrence Finch

Lawrence Finch wrote:


y_p_w wrote:


It's good practice to use your battery, but I wouldn't say that it's needed to get it down to 0%. I personally believe it's not necessarily bad to allow an iPhone to reach "0%", but others have a different opinion. 0% is not really an absolute floor. It's a reference point where the battery management system keeps reserve capacity to prevent it from getting into a deep discharge state. If it gets down to "0%" there's still enough capacity left to display an image on the screen asking the user to plug it in. I've allowed my iPhone 7 to go to 0% at least a half dozen times and after about 180 cycles it's still registering about 97% battery health. The important thing to do if it gets to "0%" is to make sure it's recharged quickly.



No, it is not good practice to use your battery. It doesn't matter whether or how much you use it. There is ZERO benefit to running it all the way down, or even mostly all the way down.


If anything, using a Mac as the power supply could mean more incoming current which theoretically can create more heat and reduction in battery life. A Mac is capable of of providing 2100 mA to an iPhone, which is more than double that of the standard 5W adapter that comes in the box with most iPhones. I personally don't worry too much about it. I allow my iPhone 7 to charge on my Mac and use the 12W iPad power adapter, where the iPhone will limit intake to 2100 mA. Once it approaches about 80% capacity it will start to back off on the input current regardless of what you're using as a power supply. It does that to protect the battery (and reduce the chance of a battery fire), since it's better to charge at a lower rate once it starts getting closer to 100%.

I'm sorry, but this is absolute nonsense. Actually, a Mac is capable of supplying only 1000 Ma from a USB port, but that's irrelevant. Even if it could supply 2100 Ma it wouldn't matter. You could use a USB supply that could provide 10,000 or 100,000 Ma and it wouldn't matter, because the phone will only use what it needs. The same way the appliances and light bulbs in your house only draw what they need. A typical house has 200 amps of incoming power, but a 60 watt light bulb will only use 0.5 amps.


Again - I never said it was "good practice" to run it all the way down. I said it was good practice to at least use it occasionally on the battery alone. I've heard of way too many devices that were plugged in all the time and the battery swelled.


And where did you hear that a Mac is only capable of supplying 1000 mA to an iPhone? That's just not true. Depending on the Mac, it will provide 1600 mA of supplemental current in addition to the standard 500 mA - i.e. 2100 mA. This is from System Report on my mid-2012 MBP right now with my iPhone 7:


iPhone:


Product ID: 0x12a8

Vendor ID: 0x05ac (Apple Inc.)

Version: 9.01

Serial Number: ******

Speed: Up to 480 Mb/sec

Manufacturer: Apple Inc.

Location ID: 0x14100000 / 22

Current Available (mA): 500

Current Required (mA): 500

Extra Operating Current (mA): 1600

Sleep current (mA): 2100

iPhone:


Product ID: 0x12a8

Vendor ID: 0x05ac (Apple Inc.)

Version:

Sleep current (mA): 2100

Mar 11, 2018 5:40 PM

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Mar 11, 2018 5:58 PM in response to y_p_w In response to y_p_w

y_p_w wrote:


And where did you hear that a Mac is only capable of supplying 1000 mA to an iPhone?

From the specs for my Macbook Air. My Macbook Pro doesn't specify the available current, but I just measured it with my iPhone 7 Plus, and it is delivering 1.5 amps, and briefly went up to 1.8 amps, so I accept your numbers. I don't know if can deliver that to more than one device, but I'll accept that it can. It definitely depends on the age of the Mac, however.


But the point wasn't what a Mac could supply, it is still about the fact that a device capable of supplying more than a device needs is not a problem and will not hurt the phone in any way, as long as it is an MFI certified power source. I routinely use a 4,000 Ma MFI certified Anker power adapter because it can charge up to 4 devices simultaneously.

Mar 11, 2018 5:58 PM

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Mar 11, 2018 8:35 PM in response to Lawrence Finch In response to Lawrence Finch

Lawrence Finch wrote:


y_p_w wrote:


And where did you hear that a Mac is only capable of supplying 1000 mA to an iPhone?

From the specs for my Macbook Air. My Macbook Pro doesn't specify the available current, but I just measured it with my iPhone 7 Plus, and it is delivering 1.5 amps, and briefly went up to 1.8 amps, so I accept your numbers. I don't know if can deliver that to more than one device, but I'll accept that it can. It definitely depends on the age of the Mac, however.


But the point wasn't what a Mac could supply, it is still about the fact that a device capable of supplying more than a device needs is not a problem and will not hurt the phone in any way, as long as it is an MFI certified power source. I routinely use a 4,000 Ma MFI certified Anker power adapter because it can charge up to 4 devices simultaneously.


Didn't you say that overnight you'll only use the 5W "ultracompact" adapter?


It's pretty well known that all the Macs with USB 3.X ports can supply 2100 mA directly to an iOS device. Now there are variations. I tried with my iPhone 7 and my iPad Mini 4 together directly to the two ports on my mid-2012 MBP. Depending on which one is plugged in first, once two devices are plugged in it reports 1500 mA to whichever one was plugged in first, then 1000 mA to the second device. So it's more than 2100 mA total, but not double the 2100 mA that it can send to one iOS device.


And yes I understand that a power supply is really just a voltage source where an iPhone's charging circuits will limit the incoming current. However, there are theoretically concerns that a higher maximum incoming current may slightly increase battery wear because of the heat. I don't think of it as a big deal; I'll trade the convenience of faster charging for the tiny increase in battery wear. If I need to use my iPhone and it's displaying less than 20% charge left, I'm not going to worry too much about it. For me that's part of the convenience of using the battery. I know there are theoretical concerns that it might slightly increase battery wear (compared to stopping it earlier), but the battery won't "turn into a pumpkin". I don't own an electronic device such that I'm babying it all the time. It's a tool with a replaceable battery.

Mar 11, 2018 8:35 PM

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Question: Does Plugging an iPhone into Your Mac Affect Battery Life?