Does it harm the battery or reduce battery life, to use the AC adaptor for extended periods while the battery is fully charged?

Rechargeable Battery - 15-inch MacBook Pro

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12 Answers from the Community

  • Best Answer:

    I have experienced the same thing, but the question remains: WHAT IS BEST TO DO INSTEAD? Leave the MBP unplugged every time the battery gets fully charged... then only plug it in when the battery is low, recharge it, and unplug it agin? Take the battery out if the MBP is to be plugged in for long periods? Do some internet research on voodoo rituals that might help battery life? Anyone have a practical suggestion on the best battery-sustaining habits to get into?

    Thanks to all...

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  • As I recently found out, yes indeed it does. I have been leaving my MBP power adapter/charger cord connected for extended periods of time, and just last week when going through the new system pref's of Snow Leopard I say a triangle with an ! inside it in the energy saver/ battery pref's. I asked a friend that works at the local Apple store about it, and his words were "Dude, you killed your battery". I now get at most an hour before the battery low warning pops up.

    And all along I have been doing the battery cycling on a monthly basis.

    Bummer Man!

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  • This is by far the best answer I found:

    well I can't enter it because it doesn't accept a link, so if you replace all the bits that I wrote in capitals by the appropriate character (except the ID bit), you'll find the thread. it is in the discussions forum.
    good luck and healthy battery life :)

    http COLON FORWARD SLASH FORWARD SLASH discussions.apple.com FORWARD SLASH thread.jspa QUESTION MARK threadID=1764220

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  • My MBP is 23 months old, and I have used it pretty much every day, all day, and some of the evenings too. Most of this is plugged in to the power. Testament to this is I have only used 66 cycles on my battery. Recently, I thought I better follow advice and do the recalibration process, which I have done twice. The first time I did this, it dropped from 90% capacity to 85%, and then down to 82%. I will not do the recalibration again!

    So from my personal experience, keeping it plugged in most of the time is a good way to keep your battery life good. Of course other experiences may differ, but until 2 months ago, I had a 21 month old battery at 90% of original charge with most of its life spent plugged in to the AC adaptor, and no re-calibration.

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  • From the looks of it this has mixed results. I have had my MacBook Pro for almost three years now. I work with it 8 plus hours a day and it is plugged in 80% of the time overnight and even when fully charged. In my experience I found that the battery cycle count hurts the reliability of the battery more than having it plugged in. I am closing in on 300 cycles after three years and in the last month I have seen the battery fluctuate in reliability. Having it go from as low as 56% to as high as 76%, and it will change every time I work with it unplugged and charge it. Also I do the recalibration of the battery every month.

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  • No. The charger appears to be smart enough to only charge the battery if it needs it. The Snow Leopard "service battery" issue appears to be unrelated.

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  • I discovered that the battery life deterioration became very noticeable, very quickly. The iStat widget currently shows 318 cycles and 'health' of 46%. With Snow Leopard, the Energy Saving window advises to replace the battery now.

    Was this useful? Answer 7

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  • I have had macbook for more than 3 years now. I always plug in charger even when I am not using my laptop. I even rarely turn off my laptop, my battery still works like new even though it has somewhere around 250 cycles. I highly suggest to plug in your charger as by doing that you create a circuit that over rides the battery and your battery stays safe.

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  • I just took my 15" A1260 into the Genius Bar because there was a message in the battery drop down menu saying to have the battery serviced. I was told I have a very now number of cycles on my battery and since it was not used much it went bad. They said to let it run all the way down as much as possible and then let it charge all the way back up when using with the ac adapter. It seems it is just as the old types of batteries where more use in good for them. They likened it to a car battery just sitting and that it would go bad. I know a car battery is a different type so don't post any juvenile comments about it.

    Now, you don't need to do this every time you use your computer, but on a regular basis like once a week would help overall.

    Hope this helps anyone get more life from there batteries and lowers the costs of ownership.

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  • my story: i have had 2 batteries completely killed by leaving the AC adaptor plugged in for extended times. the cycle count is/was/currently less than 30 on each battery. with the replacement, i barely get 30 minutes of battery usage, charging takes 1hr, but it shows up as 1000mah capacity instead of 5600mah only 4 months after replacement.

    While it could be the battery or a HW fault in the MBP, i believe it's both.

    the advice to calibrate, i.e. leave itunes/safari running on battery power for 3-4 hours, let it 'sleep', then let it deep discharge overnight for 8-10 hours while in 'sleep' mode before charging again, once a month is highly advisable. now that the laptop's out of warranty, i advise you to just suffer the yearly cost of a new battery or get the newer macbook which would have different battery issues.

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  • I've had my MBP since June 2008 and it would be mostly plugged in except for class usage. 2 years later my cycle is at about 200 and I know it's time for a new battery. So to answer your question, my battery life dropped significantly a year after I bought it. Other here seem to not have the same problem even if the battery is plugged but I have seen the difference.
    Maybe it's just my battery but it's time for a new one, sadly

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  • I got to this thread because I just bought a 2013 15" MBP and was looking for an answer to this question, (I didn't find yet, but would like to add my 2c).

    I had until now a late 2007 MBP (exactly 7 years).
    Only now, when I'm passing it on to my daughter I am replacing the original battery. (Now it needs it).
    I work at home and the laptop was almost 24x7 working/sleeping and not "extended periods" but almost all the time connected to the power. (Even when I rode my car I would have it plugged to the power). Rarely used it on battery.
    For the 1st 3-4 years I would calibrate the battery more or less every month. After that it was more like when I remembered (something like average once in 1-4 months).
    Never looked at the times that it would take to charge/discharge it, neither at cycles and so, but for those who do, now the data looks like this:
    It is 100% charged (if I unplug it, it would take something like 5-20 min to go off).
    Charge remaining (mAh): 1037
    Full charge capacity (mAh): 1037
    Cycle count: 534
    Amperage (mA): 0
    Voltage (mV): 12473

    That pretty much answers to my question (I am going to try to research it further though), if the battery in my new MBP isn't much different, I'll definitely go on having it plugged as much as I can, calibrating it monthly.
    I have no knowledge in electronics and so, but my common sense tells me that if the computer is connected to the power, I guess it has a system that bypasses the battery.

    BTW, the moment I installed Snow Leopard (several years ago) it started telling me to replace the battery. I researched the net then and found that it was the case with many other users, so I never took it seriously.

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