User profile for user: alpha754
alpha754 Author
User level: Level 1
4 points

iPhone 6S battery drain after iOS 15.8.6; how to revert?

My iPhone 6S got the notification for the iOS 15.8.6 two nights ago so I ran the update.



As you can see from the picture above, it is now playing "yo-yo" with my battery, whereas before I updated, my phone was working just fine, even if it is 10 years old by now.


You can see where it shows that it is plugged in to the wall charger, and the battery will still tank to 10%, with nothing running at all, (the phone restarts whenever the battery crashes like this, caused by the iOS 15.8.6 update) so there aren't any apps running when the phone comes back up.


How do I restore my phone from backup if the new update is playing "yo-yo" with my battery, so that I can restore/revert my phone back to the prior version of iOS that it was running, before I ran this update?

Posted on Feb 6, 2026 12:05 PM

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User profile for user: Bob Timmons
Bob Timmons
User level: Level 10
185,528 points

Posted on Feb 6, 2026 2:25 PM

Even if you could revert to an earlier iOS......(you can't).....the battery would have failed during that process as well, based on what you have told us. Try connect the phone to the wall power adapter and leave it connected for a few hours.


Try again.


If no luck, your battery was due to fail at any minute. The update might have sped things up a bit, but you will need a new battery if you want to keep the phone.


Not sure if batteries are still available for your iPhone at this point. Check with a local authorized service shop. About $75. You can find a list of authorized shops in your area using this link:


Find Locations


If no luck, you may need to try one of the iPhone "fixit" shops. You won't get a genuine battery, so make sure that you get a money back guarantee from the shop that the battery will work.


FWIW, the motherboard is now overdue to fail as well. A new battery might push the board over the edge. It happens.



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User profile for user: Bob Timmons
Bob Timmons
User level: Level 10
185,528 points

Feb 6, 2026 2:25 PM in response to alpha754

Even if you could revert to an earlier iOS......(you can't).....the battery would have failed during that process as well, based on what you have told us. Try connect the phone to the wall power adapter and leave it connected for a few hours.


Try again.


If no luck, your battery was due to fail at any minute. The update might have sped things up a bit, but you will need a new battery if you want to keep the phone.


Not sure if batteries are still available for your iPhone at this point. Check with a local authorized service shop. About $75. You can find a list of authorized shops in your area using this link:


Find Locations


If no luck, you may need to try one of the iPhone "fixit" shops. You won't get a genuine battery, so make sure that you get a money back guarantee from the shop that the battery will work.


FWIW, the motherboard is now overdue to fail as well. A new battery might push the board over the edge. It happens.



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User profile for user: alpha754
alpha754 Author
User level: Level 1
4 points

Feb 6, 2026 1:07 PM in response to KiltedTim

"If that's the original battery, it's almost certainly outlived its useful life. If the battery health is below 80%, it's done.


Unfortunately, that model is now semi-obsolete. You probably won't be able to get a battery replacement from Apple and even if you can it will cost more than the phone is worth."

Last I checked (before I ran the update), battery health was at 87%.


And yes, Apple store won't change the battery anymore, due to the age of the phone.


And I only bought this phone because my iPhone 4 died, also after trying to replace its battery as well, which is what caused me to buy this phone. (I just looked up my records and it looks like that I bought this phone in 2020, and had Apple store replace the battery for $65 CAD, in 2021.)


Prior to the update, the phone was working just fine.


The update killed my otherwise still working phone.

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User profile for user: KiltedTim
KiltedTim
User level: Level 10
226,626 points

Feb 6, 2026 12:43 PM in response to alpha754

If that's the original battery, it's almost certainly outlived its useful life. If the battery health is below 80%, it's done.


Unfortunately, that model is now semi-obsolete. You probably won't be able to get a battery replacement from Apple and even if you can it will cost more than the phone is worth.


It's time to move on. That one had a good life. Let it go.

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User profile for user: alpha754
alpha754 Author
User level: Level 1
4 points

Feb 6, 2026 1:02 PM in response to Bob Timmons

"If you have not already done this, perform a Forced Restart on the iPhone 6s


Force restart iPhone - Apple Support


Make sure that you have selected the correct iOS 15x for correct instructions."


Cannot complete.


iOS 15.8.6 update causes the battery to tank, and therefore; I can't even unlock the phone post automatic restart with my passcode before said update kills the battery again.

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iPhone 6S battery drain after iOS 15.8.6; how to revert?

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