Is It Actually BETTER To Leave MBP Plugged In All The Time?

Discussion in 'MacBook Pro' started by Amasashi, Jun 8, 2010.

  1. Amasashi macrumors member

    May 17, 2010
    In previous threads, we've established that there's no harm in leaving a MacBook Pro plugged in all the time. But now I'm wondering whether it's actually BETTER to do so.

    My reasoning is that Apple claims the battery to be good for 1,000 cycles. If I'm leaving my MBP plugged in all the time, I'm not using the battery, therefore I'm not using up a charging cycle; whereas if I use the battery to say 75%, charge it back to 100%, using it back down to 75% again, etc.. I'm slowly using up charging cycles.

  2. ziggyonice macrumors 68020


    Mar 12, 2006
    Rural America
    This is a helpful post that explains most of that question.

    I usually unplug my MBP at least a few times a week.
  3. miles01110 macrumors Core


    Jul 24, 2006
    The Ivory Tower (I'm not coming down)
    Incorrect, as cycle count is not the only factor that goes into determining battery health.
  4. h1r0ll3r macrumors 68040


    Dec 28, 2009
    As with any rechargeable battery, leaving the unit always plugged in is never good. The battery needs to cycle in order for it to "know" when it's empty and when it's full. Keeping the laptop always plugged in messes with the performance and lifespan of the battery. While it may not be the same thing, I always left my work laptop (Dell) plugged in all the time, even when I left for home. Within 6 months the battery craps out and, now, I can't go anywhere in the office without dragging my charger along too. Since it's my work laptop I could care less if that thing catches fire and explodes. But, the battery would've lasted a lot longer had I used it for a bit and then recharged. Now that you've got a pricey new Mac, might want to consider taking care of it.
  5. diablo2112 macrumors 6502

    Apr 16, 2010
    Short answer: No.

    Long answer: Batteries are complex chemical reactors. When a battery provides current, a series of chemical reactions occurs which also involves the diffusion and transport of not only electrons (current) but ions within the battery itself.

    When you charge a battery, you reverse this process. A battery degrades when it can't complete this cycle of charge-discharge-charge. Physically, a number of changes can occur which decrease battery performance, especially capacity and charge retention. The battery might leak electrolyte, various membranes can change with time and lose their ability to transport ions (such as Li+ in our MBP Li-polymer batteries) , flow-channels can develop in various membranes, the electrode materials can undergo deleterious reactions, and any number of other issues.

    Generally, when you exercise a battery, the desirable chemical reactions (such as electrode reduction and oxidation - each of the half-reactions) and the desirable transport processes ensure that the deleterious ones don't have time to consume electrodes, electrolyte, etc. Think of this as a race. The electrode materials can either follow the desired path by using the battery, or undesired ones through insufficient use. Everytime you charge/discharge the battery, it's mostly good as you prevent these undesirable reactions.

    Deep-charge/deep-discharge is occasionally good for your battery as well, as this exercises physical portions of the cell that might not otherwise contribute during light-use. [This should always been done within manufacturers specifications, as really-deep-discharge can be very bad for some batteries, especially Li-Polymer and Li-Ion cells. Modern battery management systems on our laptops should prevent this too-deep discharge process.]

    Of course, use of the battery will also degrade other elements eventually (especially membranes needed for ion transport), which is why batteries have limited cycles. The happy medium is to regularly use your battery, and when its reached its useful cycle limit, then you replace it. That will maximize performance.

    And sorry for the more detailed explanation. Perhaps I should have stopped at my short answer...
  6. monkey52892 macrumors newbie


    Feb 21, 2010
    United States of America
    Even though I am not the OP, thank-you very much for the explanation. I will be sure to keep my macbook pro's battery in tip top shape when I get it on Friday. Cheers! :D

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