iPhone 6s running slow? Consider replacing your battery


My iPhone 6S has been very slow these past few weeks, and even after updating multiple times, it was still slow. Couldn’t figure out why, but just thought that iOS 11 was still awful to me. Then I used my brother’s iPhone 6 Plus and his was… faster than mine? This is when I knew something was wrong. So, I did some research, and decided to replace my battery. Wear level was somewhere around 20% on my old battery. I did a Geekbench score, and found I was getting 1466 Single and 2512 Multi. This did not change wether I had low power mode on or off. After changing my battery, I did another test to check if it was just a placebo. Nope. 2526 Single and 4456 Multi. From what I can tell, Apple slows down phones when their battery gets too low, so you can still have a full days charge. This also means your phone might be very slow for no discernible reason. Check your Geekbench scores and see what you get if your phone is still slow!

I would love to get an official response from Apple on this issue. Be sure to read the updates to this post, especially the second one.

UPDATE: Two things:

  • Via Bryan Lee on Twitter, if you are having issues with your iPhone 6s, Apple does have a battery replacement program for certain devices, manufactured in Sept or Oct 2015. Go to this page to check to see if your device is eligible.

  • As mentioned in the linked Reddit thread, there’s a free app, called CpuDasherX, you can use to check your clock speed, see if it’s running full speed. According to this comment thread, 1848 Mhz is the factory CPU speed for the iPhone 6s.


As noted in this tweet and some of the comments, the A9 does vary its frequency based on load. So a different frequency is not indicative of a battery issue. It’s possible this Reddit thread is a red herring. Again, would love an official Apple comment.


Take a look at this free battery life wear level tester. Might offer some insight.

  • The Cappy

    Interesting. But I noticed a very large drop in performance in my 6 plus after installing iOS 11. Not especially in the mood to actually go out and buy a new battery just to test it though 😉

    • Dave Mark

      Check the update I just posted. It mentions an app you can download to check your clock speed.

      • The Cappy

        Thanks. This was an incredibly useful post. I just ran it. “In low power mode = NO” but my CPU frequency is 839.

        • The A9 has a variable frequency CPU. A variable frequency doesn’t necessarily mean anything other than variable load.

  • invinciblegod

    Can they not just update it to avoid this problem?

    • The Cappy

      What if they update it and everybody’s battery life is cut in half? Apple appears to be making a certain trade-off, figuring the other trade-off is worse. People complain much more loudly about their battery life.

      • invinciblegod

        People complain loudly of forced obsolescence too, and this to a user of the phone makes it seem like it’s true.

        • The Cappy

          In the smartphone realm, forced obsolescence seems more like a platform where getting the newest OS updates requires buying a new phone. Batteries degrade over time. Nobody designs them to do it; it’s just the nature of the thing. And new features in an OS often appear because the new chips are finally capable of doing a thing. So when you add it, older machines seem to struggle. If you and I hadn’t updated iOS we wouldn’t be having this problem. I don’t have to like it, but I don’t have to invoke the notion of an evil company designing obsolescence into a product — Especially in a case where that company seems to be doing better than the competition to extend the utility. I found if I disabled the feature that stops you from receiving texts while driving, thing improved some.

          • Mo

            I like it when I can agree with you about something.

      • DakConserve

        Then I will change the battery!

  • lkalliance

    I wonder if this makes purchasing a new 6S an unwise proposition. I was going to update my daughter’s 5S this spring, and she very much wants to keep her headphone jack, which means if I am going to get her a new phone, an SE or 6S/6S Plus. I expect that whatever phone we get is going to have iOS 11 pre-installed. Should I be wary?

    (Actually, even if I go with the SE, that’s also an A9 chip, so I guess it doesn’t matter)

    • The Cappy

      A new 6s should have a new battery. If anything, this probably means that you can discount many of the reports from people saying iOS 11 sucks on their 6s — at least to the extent that many of these complaints probably wouldn’t apply to your new phone.

      • lkalliance

        Roger that. I knew a new one would have a new battery…I mean does that suggest that a new 6S would have a shorter lifespan than it would have had a couple of years ago?

        • rick gregory

          No. As long as it’s a new battery, it will be fine.

          • DakConserve

            If they are really throttling the CPU based on battery health…

      • DakConserve

        If throttling really based on battery health, if battery health is poor, then they should provide the status under settings.

    • THX138

      iOS 11 is twice or more as slow as iOS 10 on my iPhone 6. Serious waiting time even when switching apps.

      • The Cappy

        That’s my experience too.

    • DakConserve

      The SE has the same, if not better performance then the 6S and it’s much cheaper. I am a little pissed, I just picked up an SE, but if they are going to arbitrarily throttle it…..

      This might be my LAST IPhone!

      • lkalliance

        It’s not arbitrary.

  • My iPhone 6 had performance issues immediately after updating to iOS 11. Ran CpuDasherX and it says CPU is running 600mhz instead of the 1.4 GHz factory spec.

    I checked Geekbench and my marks are approx. 50% of what the iPhone 6 should be (single-core 756 vs 2376; multi-core 1444 vs 2495).

    Frickin’ hell.

    • THX138

      New battery in this iPhone 6. It’s not battery related. It’s shit coding. I feel so dumb waiting for Siri to respond.

      • DakConserve

        Actually it is fraud, if you replaced the battery, they are just throttling the CPU period!

  • Heos Phorus

    hm… maybe they don’t do that on the 5s – that would explain why mine is still running at 1,3 ghz but the battery lost about 30-50% running time with (a clean) ios 11 install.

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    • DakConserve

      I just sold my 1 year old 5S on ebay, the upgrade to IOS 11 killed performance. I should have just rolled it back to IOS 10.

  • rick gregory

    uh… 911mhz?? WTF?

    Thank for the post Dave.

    • rick gregory

      Hmm… and now that it’s over 60% it’s 1512mhz. I wonder if it’s what that thread say it is (old, worn batteries regardless of charge level) or if it’s any battery at lower charge %.

      • This’ll make you slap your forehead: The A9 scales its frequency depending on workload, so a low frequency doesn’t prove anything.

      • rick gregory

        And now it’s 1848mhz.

        I agree with Steven Fisher – this reddit thread is BS. It has nothing to do with the battery being old.

        • I think that’s probably going too far. There’s probably an element of truth here.

          The benchmark difference is more troubling than the CPU frequency difference. Seems to me that the benchmark should be enough work to make the CPU speed up. However, then again, the benchmark might not be enough to get the CPU fully up to speed… and even if it did, it might not stay at full speed long enough to measure with CpuDasherX.

          I know, though, if I worked on iOS and I’d write code to detect if the OS was running over a faulty battery. If it were, I’d scale down and treat the battery with kid gloves to avoid a sudden shut down. (10.2.1) So checking battery state and replacing if it’s badly worn is not a bad idea at all.

          HOWEVER, don’t run out and buy a new battery if your CPU frequency looks low.

          • rick gregory

            The problem, as I think about this, is that testing needs to control variables. For example, all of the benchmarks need to be run at, at least, 100% charge and 50%. It’s possible that iOS seems 50% differently if the battery is new vs worn and thus throttles differently. That’s likely GOOD in the sense that it’s trying to let you do what you want to do without tanking your battery and leaving you with a dead phone.

          • Yup. Which is why I think you should just go back to first principles here. If your battery is mortally wounded, it’s probably impacting your enjoyment of your phone. Replace it. You’ll get better battery life. If other things happen, great!

          • rick gregory

            One nice thing is that Dave linked up a nice battery wear checker which confirms that I should replace my battery. Not URGENT but something to do soonish.

          • I asked him to add that, because we were getting too far from first principles. 🙂

  • Simon

    If this is true, it’s nuts people are only realizing now. I wonder if there is a difference between 6S phones with the Samsung or the TMSC A9.

    • Yoman

      It shouldn’t be a difference. Both have the same GHz, no? Look at what it says: “Although it was speculated that the Samsung version had worse battery performance than the TSMC version, multiple independent tests have shown there is no appreciable difference between the two chips”.

  • Please don’t take this post that seriously.

    CpuDasherX tells you the current CPU speed. iOS rolls that up and down as needed on the 6S and SE. A low CPU speed doesn’t mean your battery needs replacement.

  • My 6s went to complete junk immediately after ios11. It’s gotten slightly better with updates but not much. Same with my wife and her 6.

    • rick gregory

      So here’s a weird anecdote. My 6S Plus was fine after the update but 11.1 started to have terrible battery life. I’d leave the phone overnight and it would go from 90%+ to 1%. Clean install… nada. Left it alone for a few days… no bueno. Then… it cleared up at about 10 days in.

      Did a misbehaving app update and fix something? Did the OS finally do something? No idea. Only time something like this has ever happened to me too. It’s on 11.2 now and is still fine.

      All of this is to say that aside from doing all the standard stuff (look at Battery in settings and see what’s using battery, grab a Status app to see whaat % of CPU is being used, update apps…) That maybe yours will clear up. At the least, I’d update to 11.2 and all your apps if you’ve not. Good luck.

  • I did a complete wipe and reinstall to 11.2 from scratch on my iPhone 6 last week. Soooo much faster and responsive now. Everything that used to take a few more seconds than I remember, just pops up now. Definitely recommend that if your having issues.

    • THX138

      Will do this week. My iPhone 6 is a joke on iOS 11.

      • THX138

        Update: I did a factory restore and spent the 3 hours or whatever making sure I had backups, etc. The iPhone 6 is now running much better. Not as fast as iOS 10, but I’m not banging my head against the wall. So, if you’re suffering from always very slow performance, factory restore.

  • THX138

    iphone 6, slow as molasses. 9 seconds to open Podcasts. Seems that ios 11 uses more memory than ios 10, and hence the memory is purged more often. Switching between ‘open’ apps can take 6 seconds before I see a screen. Also, some apps open but suspend for 5–20 seconds before they can be used, because they’re synching and in the meantime can’t be used. Siri went from a quick click on the home button to now showing pretty graphics and 10 seconds later: Siri is available. A disaster of an upgrade. If you haven’t already upgraded from iOS 10 to 11, don’t.

    • fastasleep

      There’s something clearly wrong with your phone or iOS install. I was running iOS 11 on my 6 before I got my X, and aside from a little hiccup here and there with animations and what not, it was totally fine. Used Podcasts all the time with no delays like you’re reporting. Something else is wrong.

      • THX138

        I factory reinstalled before upgrading from 10.whatever to iOS 11.1, because I know how Big .X releases are. I kept expecting every new 11.1.x release to speed up the system, but nope. 11.2 also disappointed. I’m gonna spend a while removing the apps I don’t need, then do an iTunes backup, then factory re-install. If the factory install gives me the zippy, then I’ll restore and see how things go. If the restore gives me poor results, I’ll manually restore the apps and data I need. That said, animations should be silky smooth, and I run my iOS devices with all the animations off…

        • THX138

          Update: I did a second factory restore and spent the 3 hours or whatever making sure I had backups, etc. The iPhone 6 is now running much better. Not as fast as iOS 10, but I’m not banging my head against the wall. So, if you’re suffering from always very slow performance, factory restore.

    • Podcasts was one of the apps that was super slow for me. Doing the wipe and start from scratch has improved it immensely.

      Prior to my wipe/reinstall I was trying to figure out how to afford a new phone. But now I am really happy with the performance of my 6 and it’ll probably last a couple more years.

  • DakConserve

    What a joke, Apple has kind of destroyed any trust I had in them. I can change the frigging battery, if I knew it was actually failing.

    PS. Is the CPU frequency decrease based on ACTUAL battery health or your phone model or serial number? Seriously.

    What a joke!