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Released September 25, 2015. Model A1688/A1633. Repair of this device is similar to previous generations, requiring screwdrivers and prying tools. Available as GSM or CDMA / 16, 64, or 128 GB / Silver, Gold, Space Gray, or Rose Gold options.

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CPU slow when battery low!

Hi,

This week I’ve placed 4 new OEM batteries into 4 iPhone 6S’s. All 4 customers came back with the same issue: when the percentage goes below 20%, the phone starts to lag so much they cannot use it anymore. As soon as it is plugged into a charger, the issue disappears.

For the past 7-8 years, i’ve been repairing iPhones, and last year alone I’ve replaced at least 70 iPhone batteries without any complaint. January and february i didnt do any repairs because of work abroad, and now in march i get all this trouble. Could this be because of iOS 11.2.6? Is this an extreme case of CPU throttle? How can i reset this? Will iOS 11.3 fix this?

I hope someone can clear this out because this seems like Apple trying to eliminate 3rd party repairs!

Thank in advance

Answered! View the answer I have this problem too

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Have you had any success with alternative batteries? After having this same problem with a battery from an eBay seller, I have just ordered a non OEM battery from Replacebase. I’m now wondering if I’ll get the same problem.

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9 Answers

Chosen Solution

I wonder how good some of these replacement batteries really are. With the high worldwide demand in 6S batteries, Apple is taking all of the good stuff and what's left might not be so good. Heck, even Apple has struggled with batteries.

Batteries performing poorly when at 20-30% of charge is a classic case of dead or dying batteries. I would talk to your supplier about this as it may be more indicative of poor batteries than an iOS issue.

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These batteries came from Replacebase, a reliable source that hasn’t let me down in 4-5 years. Some other batteries came from a Chinese supplieer that also sells me 100% original screens (Apple logo on flex, pearl green shine around camera hole etc). I trust both these suppliers.

I’m just hoping that some other technician can replace a battery in a 6S on iOS 11.2.6 without having this problem.

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I don’t believe this is the same issue as the CPU throttling Apple have admitted to. In this case the lagging is so bad the phone is essentially unusable, can’t launch apps and can’t even make phone calls, and if any audio plays it can be scrambled.

In this case the CPU is still at maximum frequency but the reason for the lagging is the CPU is at 100%.

I’ve noticed it on my 6s on iOS 12.1, when battery goes under 20% and I go on an area of no mobile data (or turn off mobile data to simulate) then CPU goes to 100% and battery drains down to zero in no time.

You can use Lirium Info Lite to see the CPU usage (CPU Dasher X does not show the total CPU usage so don’t use that). I’m a developer so trying to figure out what process is responsible for this. The moment the phone is connected to the Mac it isn’t possible to debug the problem because it also starts charging which immediately resolves the issue, however enabling network in the Devices window allows it, and can use Instruments to view the process list with CPU usage. It’s hard to tell because the monitoring processes consume a lot of cpu but it seems the culprit is the kernel, which usually means high disk access but it could be an issue with reading info from a 3rd party battery I suppose. That is my current theory that when the battery goes low iOS begins to try to read info from the battery or read it more frequently and since the 3rd party battery does not support whatever it is doing the kernel goes to 100% cpu. I’ve seen a similar behaviour with the Blackberry email app if you read its reviews you’ll see.

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This should be the answer

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Apple did it and here is their apology and remedy after they got caught:

https://techcrunch.com/2017/12/28/apple-...

Apple is reducing the price of an out-of-warranty iPhone battery replacement by $50 — from $79 to $29 — for anyone with an iPhone 6 or later whose battery needs to be replaced, starting in late January and available worldwide through December 2018.

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This is IFixit, not MacRumors. What can an Apple Store do that we can't?

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apple repair I can't compete with that price, can you? This isn't the first time in history that the big guys have put the little guys out of business https://fee.org/articles/41-rockefellers...

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Have you told customers with this issue to make an iTunes backup of their phone, restore it and see if the issue persists?

You can tell them to restore the backup later after testing that the phone works fine after restore before restoring the backup.

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My issue with my iphone 6s started to lag and cant even use it when it gets below 50% health. This started after the 11.3.1 update and has never done this before even after i changed the battery with a unbranded generic battery. Which i had ran a battery test on it and its only at 19% wear.

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i'm starting to see this with my 6s too < 55%. i verified the clock speed was being adjusted (again) on 11.4. however i also noticed [with a 3rd party battery app] that the battery was between 13% - 18% wear (it was 13% yesterday, suggests 18% wear today after a full charge). i got the replacement battery Dec, 2017 and i wonder if it's not a bad rash of batteries (given the timing) for 6S owners? (eg: we all got them around the same time and it was a bad batch?).

the kicker is; it seems to perform OK in low power mode (which appears to halve the clock speed?).

that or the internals aren't reporting the correct stats with the new updates to the OS because it's a non-apple battery(?). i'm on month 7 of this battery (and i don't use the ph a lot during the day) so it's hard to tell.

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It looks like the software in iPhone when the battery is replaced with a ‘non-genuine’ battery the iOS reads it as needing serviced even though the battery is brand new.

I suspect this to be due to the daughter board/ic in the battery to not have been programmed by Apple.

Further to this, I suspect this is Apple’s way of lashing back at the repair community for outing Apple for slowing down older phones with potential battery issues.

Not too sure if Apple will rectify this issue, I doubt it as Apple may cite safety concerns as it is a lithium part.

The issue thus far doesn’t appear to affect IPhone 5S/6 or Iphone 7 and above, just IPhone 6S strangely. Could be a test bed to see if it’s affecting us..

If you would like to test your batteries without Apple’s beta software in iOS, we use Coconut Battery (Mac) which reads the battery directly and is much more accurate. Gets you a cycle count and a load of other data, very handy.

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Hi dear,

did you get solve the problem , i am having the same problem in client’s iphone 6s after change the no OEM baterry, any good results to solve it ?

Best REgards,

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I just answered your question below I think it should solve your problem, I had the same problem!

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I had the same problem, I have a iPhone 6s and had a mobile defenders battery and every time it reached 7% it would slow the phone so much it wouldn’t be usable, the animations would be at 25% speed. When I would go to the battery health (beta) under setting I would get “service” I went through around 4 battery’s until I got so sick of it that I ordered one from another company (injured gadgets) and it worked perfectly. I think it is based on where you get the battery because the cheap battery’s that some company’s get don’t work. Also with the battery from injured gadgets, when I went to battery health (beta) in settings it said 100%.I hope it works for you this was so unbelievably frustrating and I was so happy when I used another company to supply the battery because the phone worked all the way down to 0%. Ps I am not trying to plug injured gadgets in any way I am not affiliated with them but their battery’s worked for me so they might be good for you. If you have any questions feel free to reach out!

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I can tell you from experience having my iPhone battery replaced, if it says serviced or needs service you need to take it back to the place and replace it with a battery another battery the battery you received is faulty they will swap it out it fixed my problem

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