CPU slow when battery low!

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.

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.

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.

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.

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,

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!

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

iPhone 6s. Mine was/is slow and lagging anywhere under 50% battery. After reading some of your answers in here, as I had no clue, I plugged the charger in, and it seems ok again. I’m not convinced a new battery will help, but I cannot only use my mobile when it is charging. Anyway thanks for all your replies, it does help in the meantime, as without the charger plugged in it was just about unusable.

Have the same Problem here with an 6S plus. It has got an ifixit battery as replacement and it says service in the battery settings. But testing the battery says it has more than 100% power compared to the original apple.

Should I try to replace it again?

I have also experienced this problem. When the battery level drops below approximately 20%, the phone begins to lag. In this state, if you use power-intensive software or processes like filming with the camera, the phone completely freezes, suddenly blacks out, or turns off entirely. However, as soon as you plug the charger in, even if the battery is at 1%, it returns to normal and works very well.

I believe this issue is related to both modern battery quality and iPhone updates themselves.

Technically, when a battery is fully charged, the voltage is higher—around 4.2V and when it completely drained it must be around 3.7. A higher voltage can increase processing speed and also decrease amperage, which is beneficial as it produces less heat. Standard operable voltage for iPhone is 3.7 to 4.2. As the battery percentage decreases, so does the voltage, and it should typically reach to the lowest operable voltage of 3.7V for the iPhone to still function properly.

The problem arises from the fact that some low-quality batteries cannot maintain a stable 3.7V when their capacity falls below 20%. Or, to put it more accurately, after a few months of use, they can no longer do so. This is the root cause.

Today's market is flooded with counterfeit batteries. Their producers manipulate them to always display 100% health, even after two years of use, which is impossible.

The second reason stems from iOS updates. Apple intentionally decreases processing speed through updates for older phones to encourage users to buy new ones. I had an iPhone 3gs that I never updated, and it had no problems. However, not updating is not a feasible long-term solution, as we need to update apps to keep them functional.

I have a solution for the battery-related issue that worked for me and might work for you. Stop using the original 5V-1A iPhone charger. Instead, use a high-quality fast charger 20-25. These chargers can provide higher power levels (e.g., 5V/3A, 9V/2A, 12V/1.5A) altogether. Using such a charger seems to stimulate the battery, enabling it to maintain a stable voltage above 3.7V even below 20%. I recommend trying this method.