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Studying the Slow Decay of a Laptop Battery For an Entire Year 363

First time accepted submitter jradavenport writes "I've been keeping a log of the health of my MacBook Air battery for the past year, taking samples every minute I use the computer (152,411 readings so far!). This has allowed me to study both my own computing/work habits, but also the fascinating rapid decay of battery capacity. Comparing it to my previous 2009 MacBook Pro, the battery in this 2012 Air is degrading much faster."
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Studying the Slow Decay of a Laptop Battery For an Entire Year

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  • by fuzzyfuzzyfungus ( 1223518 ) on Thursday August 15, 2013 @10:55AM (#44573651) Journal

    You're discharging it wrong, don't do that.

    • by Anonymous Coward

      He finds the failure of a product he paid good money for fascinating, rather than infuriating.

      • It's not necessarily a failure at all, just different. A 2009 MacBook (especially with the removable battery) used older technology, but did not store nearly as much energy per cm^3.

        A 2012 Air uses a much more compact battery, that holds more power, and gets hit a lot harder by newer processor features. (Cause a new processor uses more juice when running, but then sleeps more often) The overall curve of usage isn't going to be the same with all those tech changes.

        • The short peaks of power usage that new processors do should be pulled from a few electrolytic capacitors and a few tantalum capacitors (for those pesky ns power drains).
          A Pentium 4 pulled about 70-90 amps peak. No way that came directly from the powersupply. There was a large array of capacitors on each motherboard to buffer for those power draws. Inside the socket was an open space. Usually there were a few high speed capacitors there to buffer for the fast pulses.
          Newer processors will have a similar p
  • Survey says... (Score:5, Insightful)

    by djupedal ( 584558 ) on Thursday August 15, 2013 @10:57AM (#44573685)
    Let's see the comparative graph where you did identical tracking over time for both, instead of detailed now against casual before, which seems a bit weak. I'd also like to see how you factor out the constant logging's effect as well.
    • Re:Survey says... (Score:5, Informative)

      by BoRegardless ( 721219 ) on Thursday August 15, 2013 @11:09AM (#44573831)

      We live with what we got now. That is life. But ...

      Within a few years that will change with lithium-sulfur batteries if the lab geeks have anything to say about it. []

    • Re:Survey says... (Score:4, Insightful)

      by Nadaka ( 224565 ) on Thursday August 15, 2013 @11:16AM (#44573899)

      Yea. a change in methodology between test invalidates the results of an experiment. It could very well be that running the battery test every minute is causing his battery to deteriorate.

    • Re: (Score:3, Interesting)

      by AmiMoJo ( 196126 ) *

      While hard data would be nice we can reason that his results are unsurprising.

      The older laptop was a more conventional type and thus would almost certainly keep the batteries a bit cooler than the newer, ultrabook style one. Heat accelerates the decline of batteries. I'm not surprised by this result.

      PROTIP: Remove your laptop battery if you are running from the mains most of the time and keep it in a cool drawer somewhere.

      • Re:Survey says... (Score:5, Informative)

        by aclarke ( 307017 ) <spam.clarke@ca> on Thursday August 15, 2013 @11:48AM (#44574315) Homepage
        PROTIP: MacBook Air batteries aren't removable (in that sense).
      • For devices using Li-Ion, try and adjust your charger settings so that the battery has to drain down to 85-90% (instead of 95-98%) before a charging cycle starts. Fewer charging cycles per year gives you more years out of the battery.

        This trick works best if you spend most of your time hooked up to external power. But is still beneficial for devices that get left plugged in for a few days at a time between bouts of heavy use.
      • by pepty ( 1976012 )

        PROTIP: Remove your laptop battery if you are running from the mains most of the time and keep it in a cool drawer somewhere.

        YMMV. Most of the heat a removable battery (i.e., designed to be easily removed by the user) experiences occurs due to charging/discharging, since the battery doesn't overlap the hot parts of the motherboard. I never bothered because it is so easy to dislodge the magsafe connector on macbooks.

        • Re:Survey says... (Score:5, Informative)

          by gnasher719 ( 869701 ) on Thursday August 15, 2013 @12:39PM (#44574889)

          PROTIP: Remove your laptop battery if you are running from the mains most of the time and keep it in a cool drawer somewhere.

          MacTip: DON'T. Your Mac automatically scales back its clock speed to 1 GHz tops. Brownouts can crash your computer immediately because there is no battery to supply power. Magsafe connectors and no battery are an obvious bad combination. And you'll get dust into your computer.

      • by tibit ( 1762298 ) on Thursday August 15, 2013 @02:41PM (#44576071)

        It shows that you don't know the details of Apple's power delivery architecture. Magsafe-equipped Apple laptops are intentionally crippled in that the charger is artificially disabled if you use an unauthorized one. There's a chip in the magsafe plug that connects to the middle pin and is interrogated by the system management on the mainboard. If the interrogation fails, you can still use the power source, but the charger is disabled.

        All it takes not to charge the battery is to cover the middle magsafe pin. I've done it by keeping in use one charger with a bad magsafe plug where the chip had died. Died how? Ah, exposure to the saliva of a 1 year old, he liked to lick those plugs, they admittedly taste "funny" since they are energized :)

        That way you have the best of both worlds: you don't lose your work if the magsafe plug is kicked loose, and you don't charge the battery if you don't want to. Win-Win.

        • by AmiMoJo ( 196126 ) *

          It's not the charging that is the issue, it's heat from the laptop. If you removed the battery and just stuck it in an oven at say 40C it would degrade. Batteries are chemical devices, they react to temperature.

  • by geek ( 5680 ) on Thursday August 15, 2013 @11:00AM (#44573717)

    I got 10 hours of battery life on my 2011 macbook air when I first got it. I don't just mean 10 hours of it sitting idle either. I could get 7 hours of continuous play of movies. Then Mountain Lion came out and I was lucky to get 3 hours tops. That lasted 6 months until they "fixed" it and I was able to get 5 again. Now in I can consistently get 4 hours with it sitting mostly idle.

    I love the machine but I hate that I cant change the battery myself. I'll have to pay the Apple tax to get this fixed. I am holding out hope for Mavericks though, hopefully the power saving features can breathe some new life into this thing.

    • Yikes--same format movie played on both laptops = differing battery lives? Definitely sounds like an OS power bug (or several), unless the movie formats differed (lower vs. higher qual). And if not that, the minute possibility remains that someone in the processor architecture team made a tradeoff in the graphics hardware that didn't work as intended.

      Going from 7 hrs active to 4 hrs idle is depressing :(

    • by h4rr4r ( 612664 ) on Thursday August 15, 2013 @11:15AM (#44573893)

      What do you mean you can't change the battery?
      Do you not own a screw driver? And you call yourself a geek. []

    • Did they change anything in the graphics drivers with the OS update? I wonder if maybe hardware acceleration on video either got knocked offline or became really inefficient.

    • by samkass ( 174571 ) on Thursday August 15, 2013 @11:26AM (#44574021) Homepage Journal

      I love the machine but I hate that I cant change the battery myself. I'll have to pay the Apple tax to get this fixed. I am holding out hope for Mavericks though, hopefully the power saving features can breathe some new life into this thing.

      If you are willing to unscrew two dozen little screws, the battery swap-out is actually pretty easy according to iFixit. Of course, the battery itself will cost you over $100 bucks new, and Apple only charges about $120 installed, so the only real reason to do it yourself is if you live far away from an Apple Store and don't trust a carrier service with your laptop.

      • Re: (Score:2, Insightful)

        by geek ( 5680 )

        Yeah, I dont want to void my warranty either.

        • Re: (Score:3, Funny)

          by h4rr4r ( 612664 )

          You don't want to void a warranty and you call yourself a geek?

          How much did you pay for that UID on ebay?

          Warranty will be expired by the time most batteries will be needing replaced.

    • by tlhIngan ( 30335 ) <slashdot@w o r f . n et> on Thursday August 15, 2013 @11:30AM (#44574059)

      I love the machine but I hate that I cant change the battery myself.

      Yes you can, and it's not that hard [].

      You know what the hardest part of it is? Going to ifixit, getting the screwdriver, and clicking "checkout now".

      8 screws for the bottom cover, and 3 more securing the battery to the case. OK I take it back, the hardest part is possibly removing the bottom cover - Apple does use rather strong clips.

      The same is true for everything OTHER than the MacBook Pro Retina 15", which has annoyingly-glued in batteries. I think the 13" is on a carrier frame.

      It definitely isn't rocket surgery.

      • This seems like a lot of work. I like laptops that allow me to push a switch and drop out the battery and swap in the spare in about 5 seconds...which would be almost every other laptop in the world other than ones made by Apple?

        • Re: (Score:3, Insightful)

          by SuperKendall ( 25149 )

          Those laptops also get hours less battery life. I'd rather have a laptop taht works great for three-four years and then requires a battery change once, than one where I'm swapping out batteries weekly.

          I also had Mac laptops back when you could pres a button and remove the batteries. The batteries generally lasted only a year, then were worthless and had to be replaced.. go back to that world? No thanks.

    • by Bogtha ( 906264 ) on Thursday August 15, 2013 @11:31AM (#44574079)

      If your battery was great until a software update, then the problem probably isn't the battery but the software, and replacing the battery won't solve your problem.

  • I seem to be constantly fighting the battle with battery life, and it is a topic that I am acutely worried about, thanks to the newest generation of phones which seem to have settled on non-replaceable batteries. I found this very interesting. Glad someone took the time to take these measurements and write it up.

    • They are considered disposable and if you can make it until the next upgrade cycle/treadmill they don't care.

      For those of us who actually buy our phone outright, it sucks.

      • by h4rr4r ( 612664 )

        What do you mean non-replaceable?

        Do you not know how to work a screwdriver?
        Lefty loosy, righty tighty. You can order the battery and driver online if the latter is an oddball shape.

        • With voided warranty.
          And that's assuming you can find the replacement parts for your model, which isn't straightforward for anything other than iphones.

          • by h4rr4r ( 612664 )

            If it was under warranty you could have them do the work for free. So which is it? You are under warranty and don't need to worry or you are not and voiding it does not matter?

            Bullshit, I have found parts for many smartphones, including screens and power ports. No different than getting ebay laptop parts.

            • by h4rr4r ( 612664 )

              I would also like to mention that I opened and inspected a Nexus 7. When I found out that unit was still under warranty I returned it and they fixed the issue free of charge. So the warranty clearly was not voided.

          • If it is still under warranty then the manufacturer gets to replace the battery if it is out of warranty then I pay either way.
  • Nice to have if the power goes out unexpectedly, but shut down ASAP.
    • That's not really the point of a laptop battery. Also, doesn't leaving it plugged in all the time kill the battery faster than anything?

      • For a few reasons:

        #1 is because most (all?) Li-Ion batteries can only be charged a few hundred times. Even a partial charge from 95% back up to 100% can count as a "charge cycle". So one tactic is to change your power management settings so that it doesn't start a charge cycle until the battery hits 80-90% levels.

        #2 is heat.
  • Your software is querying the battery, which in turn takes battery power. If you keep asking it to check on itself every minute, you are decreasing its life expectancy in so doing. While it wouldn't produce as rich of a data set, if you really want to know how long your battery lasts at idle, you need to track it with pen and paper.
  • by spamchang ( 302052 ) on Thursday August 15, 2013 @11:10AM (#44573845) Journal

    Most modern lithium batteries should *not* be cycled or discharged "fully"--such a practice degrades the battery capacity quite rapidly. I think the practice of fully discharging the battery comes from the NiMH-type rechargeable AA(A) batteries.

    Yeah, sometimes people recommend fully discharging a lithium battery during operation so that the monitoring software can recalibrate it's battery power meter to adjust for the decline in total capacity, but I'm not sure it's worth it.

    As mentioned earlier, temperature is a big factor as well. Maybe Haswell will save the day...

    • No modern li-ion battery will let you charge or discharge it far enough to cause actual damage. You can treat them however you like cycle-wise and you'll get about the same total lifespan out of them. Using the battery and how long has passed since manufacture are by far the limiting factors.

      • by PPH ( 736903 )

        No modern li-ion battery will let you charge or discharge it far enough to cause actual damage.

        Tell that to Boeing.

    • by csumpi ( 2258986 )

      batteries should *not* be cycled or discharged "fully"

      It depends on what you mean by "fully discharged".

      Yes, if you discharge a LiIon battery completely to 0V, the battery will be damaged. This is why all LiIon batteries (should) have a battery management system [] that monitors the battery's voltage and cuts off power once the voltage falls below a certain level, somewhere around 3V per cell for LiIon.

      I use LiIon batteries in RC cars with the cutoff voltage set to 3.2V/cell and the batteries stay within a couple % of their original capacity even after disch

  • Perfectly valid (Score:5, Informative)

    by Russ1642 ( 1087959 ) on Thursday August 15, 2013 @11:24AM (#44573997)

    I love studies with a sample size of one. No statistics, no variability. Definitive.

    • by geek ( 5680 )

      Its not a study. It's just someone monitoring their own laptops battery life. Lighten up.

    • Re:Perfectly valid (Score:5, Insightful)

      by Sockatume ( 732728 ) on Thursday August 15, 2013 @11:34AM (#44574121)

      Yes, because the author insisted that it was the definitive study on how all Macbook batteries behave, so we've got to hold him to that standard. I'll go further: this cad didn't even have this published in Physical Review Letters, much less Science or Nature. He didn't even get it peer reviewed, and... my God, there's no conflict of interest statement! Who was his ethics board?!

      Sweet Jesus, I'll bet he isn't even working in a laboratory!

    • by Twinbee ( 767046 )
      It may encourage a more definitive study, especially if many others have reported similarly bad battery life for the air.
  • Almost every iPhone on record has been more likely to shatter its screen than the one before it. Apple went from 1st in lowest malfunction rates to 6th from 2007 to 2011. The new ipad is heavier, runs hotter, and gets worse battery life than the one before it. This isn't exactly a new pattern that the battery in the new air is inferior. Everything Apple is going downhill.
    • by h4rr4r ( 612664 )

      That is because each one is more scratch resistant.
      Android phones are the same, I only own those actually. The harder the glass gets the more brittle iy is.

      Their malfunction rate went up with volume, not really surprising. I hate to be defending Apple, but you are being rather unfair.

  • by SuperBanana ( 662181 ) on Thursday August 15, 2013 @11:30AM (#44574063)

    Calculated battery capacity is an estimate, nothing more, used by power management to decide when the computer should be force-slept, then suspended to disk to keep from damaging the battery (ie, it's not useful to wake up too late from sleep to do the suspend-to-disk.)

    The SMC's estimate is just that: an estimate. Errors build up over time, and certain things fake it out a bit. For example, note the capacity, unplug the laptop, use it for 30 minutes, plug it in. Immediately the value will be different. It'll change again when fully charged. Your battery capacity didn't actually change. Even in a perfect world, since batteries have internal resistance, capacity gauges can never be perfect(if you draw at X you'll get less power out than if you draw out at X*0.8), and the battery's capacity varies with temperature. Battery degradation is impacted by temperature as well, so unless you're controlling for temperature of the pack, this was a completely useless endeavor. The only way this would have been useful would've been to cycle several (probably a dozen or more) batteries on lab-grade equipment in a temperature-controlled environment.

    The noise and big upward swings alone should tell you that using the SMC's estimate for the purposes of statistical analysis or trending is virtually useless.

    The stupid shit I see "enthusiasts" of any product obsess over is absurd. The time wasted on such an exercise far outweighs the impact it possibly could have had on the author (and probably even 9-10 other people combined.) The batteries last for well over 6 hours. Most people using a ultrabook with the battery life of a Macbook Air have plenty of opportunities to charge their machines during the course of a day.

    • by ssam ( 2723487 ) on Thursday August 15, 2013 @12:13PM (#44574591)

      You get around the error in the estimate by looking at a large number of readings. There are plots showing that the style of usage has not changed with time, so I don't see how the downward drift could be caused by something like sampling when the battery is full or when its empty. I am also fairly sure that when you do a full cycle that lets the battery controller recalibrate. The 'study' may not be perfect, but I have never seen a better one (studies on discharging cells at constant currents and temperatures don't tell you all that much about laptops).

      Yes temperature is an issue for batteries. But the temperature of a laptop battery is dominated by the design of the laptop, and how much current is being drawn (or charged) to it. Maybe the previous macbook pro was only used in a aircon'ed office and the macbook air is being used in a steel mill, but i think that would have been mentioned.

      This study only covers 2 laptops (and only one in high detail), but its worth 10 times all the battery anecdotes that you hear around the web because it contains measurements. I hope some more people try his script, and post the results.

  • My laptop is rarely off AC power. When I had the charger set to stop charging at 100% (and to recharge when 90%), my battery life greatly improved. OId battery dropped 60% in reported capacity in less than 2 yrs; new battery is barely down 30% in the following 4 years.

    I call it Chinese electron torture for your battery -- drip, drip, drip.

    I don't know how OS X controls battery charging, but all OS's should provide an option to stop charging at 100%.

    • For new laptops these days, we use 80% or 85% as the threshold before a charge cycle takes place. The default for Lenovo is 96%. Most of our users spend 80% of their time tethered to a power cable, and charging every few days after it trickles down to 96% is just silly (and bad for the battery).
  • Without knowing how deep the cycle was. Furthermore, the rate of discharge and temperature during the discharge will also have a fairly significant affect.

    Basically, you will get about 1/10th the charge cycles out of a battery that is nearly completely discharged vs one that is only discharged to 10%.

    Its better to really think of LI as providing a fixed number of watt hours. You can consume them in small bites, or you can consume them in big chunks but once you consume them they are gone.

    The best rule for l

  • Maybe I'm a bit exaggerating here but, man... Anyone can measure how long the battery of a laptop lasts, but this guy actually put some effort to patiently capture the values long-term and, making the graphs of the battery decay and his computer use times. Good stuff, interesting report!

"This is lemma 1.1. We start a new chapter so the numbers all go back to one." -- Prof. Seager, C&O 351