Bought new MBP, advice needed on power/battery usage

Discussion in 'MacBook Pro' started by Agnel, Apr 15, 2010.

  1. Agnel macrumors member

    Apr 13, 2010
    Hey folks,

    Just got the 13" base model yesterday and it suites my needs very well. I did read about the battery cycles and calibrating the battery, but I still didn't get a clear answer as to when to charge it.

    I'll be using this MBP at home most of the time say 8 to 10 hours a day, and might carry it to college occasionally. So these are my questions.

    1. Should I keep the power adapter plugged in even if it is fully charged?
    2. Or should I charge it fully, then let it completely drain, then charge it again?
    3. Will keeping it connected to power all the time save the battery life(cycles)?

    Thanks in advance.
    I never really bothered about the battery life much, but on MBP I thought I'll do what is right. :)
  2. vong macrumors 6502a


    Jan 31, 2010
    1. no apple advises that you do not leave it plugged in while it is fully charged.
    2. do that, let it drain then recharge it.
    3. not sure
  3. Agnel thread starter macrumors member

    Apr 13, 2010
    Thanks for the replies.. guys. Appreciate it.
  4. rouse2 macrumors newbie

    Oct 6, 2008
    I don't see anything about leaving the laptop plugged in when not in use on the page that waloshin references (though I may be missing it). Furthermore, in my experience Macbook Pro's are horrible at preserving battery life when asleep. A thread in MacRumors reported an average of about 2% drain per hour and that roughly matches my current Macbook Pro. Leave it unplugged for 2 days and its basically dead. The drain on my 6 year old dell over the same 2 days would be negligible.

    Also, my understanding is that the Mac batteries are very smart and that they drain specific cells independently so full discharge and recharge will happen under typical usage without having to worry about really running the system to the death point.
  5. archdelux macrumors 6502

    Oct 12, 2008
    Why is that? What happens to the battery if it is left plugged in for prolonged periods of time on a full charge?

    Also - anyone know the answer to the OPs 3rd Q?
  6. vong macrumors 6502a


    Jan 31, 2010

    i read it in the forums somewhere, forgot what happens though. i just skimmed through it.
  7. Agnel thread starter macrumors member

    Apr 13, 2010
    Exactly, that's my question.
    I've been using my NEW MBP for the past 4-5 hours on battery after charging it fully through the night. It never showed 9hrs of battery even once.

    It kept varying between 4 - 5 hours... initially, now it is around 2 hours. :confused:
  8. Pax macrumors 6502a

    Dec 12, 2003
    1. Up to you. The Mac disconnects the battery from the charger when it is fully charged. Then it "floats" without any voltage being applied to it. So there is no practical difference from a battery point of view between leaving the Mac plugged into the charger and unplugging it. Apple does not specifically recommend unplugging it. Read the page carefully. IIRC it says if you leave it plugged in a lot, unplug it once a month and calibrate the battery.

    2. not recommended, see above. Nothing on the Apple page recommends this more than once a month for calibration

    3. Yes. But it in theory it might slightly shorten the battery's life through other mechanisms

    Note:- calibration is nothing to do with battery longevity. IIRC the Apple battery page says that calibration is to make the on screen displays more accurate; and to increase the "efficiency" of your battery. It doesn't define efficiency, but it is probably power out / power in ie squeezing more charge in. The Apple battery page does not mention longevity, or lifespan, or anything like that.

    In short:- Just use your Mac. The battery will take care of itself. There are various voodoo things which in principle might slightly "improve" battery longevity, but (a) they're very complicated and (b) there is no clear evidence that they will materially improve longevity. They also might decrease longevity. has some good info on charging & discharging Li-ion batteries. An interesting read.

    My Macbook has been plugged into its charger 22-24 hours a day for 3.5 years. It has 350+ cycles on it and is still at 90+ %. I have never calibrated it. It still runs the Macbook for about 3 hours, close to what it did from new. Just use it.
  9. Puqq macrumors regular

    Oct 18, 2009
    Sorry, but this is incorrect.

    You have to unplug the battery time after time and let it fully discharge. However, you don't have to do that every day (monthly maybe). The computers are protected from overcharge issue. The drivers basically slow down the charging process after certain checkpoints.
  10. Fisketryne macrumors newbie

    Apr 14, 2010
    Are anyone taking statements like this for fact? How about a link/source? Especially when every other poster seems to say different things.
  11. Josh.C.123 macrumors member

    Oct 26, 2009
    i charge it fully and then drain it... i think this is the better option.
  12. Agnel thread starter macrumors member

    Apr 13, 2010
    I'm getting nearly 7-8 hours of battery on the 13 inch MBP for casual browsing and chatting + reading a pdf. The power details in the system profiler also helps.

    Thanks for the replies guys!
  13. snaky69 macrumors 603

    Mar 14, 2008
    Just use the thing and stop worrying about it. My pre-unibody MBP is going on 3 years old and the battery still lasts me around 3 hours, it's plugged in all the time when I'm at home and I bring it nearly daily at school.
  14. mark28 macrumors 68000

    Jan 29, 2010
    This is without turning down the brightness and switching off blue tooth and whatever most people do to get high battery life?
  15. Agnel thread starter macrumors member

    Apr 13, 2010
    Turned off Bluetooth, no keyboard lights for 5 hours(was on for first 3 hours), no DVDs, no YT videos, just normal browsing... and brightness was at 50-60%.
  16. Agnel thread starter macrumors member

    Apr 13, 2010
    Pax, Thank you so much.

    I tried running it on charger... the charge capacity hasn't changed much, but running from battery reduces the full charge capacity. I guess.. I will try to drain it out once a week/month.
  17. Pax macrumors 6502a

    Dec 12, 2003
    "No trickle charge is applied because lithium-ion is unable to absorb overcharge. A continuous trickle charge above 4.05V/cell would causes plating of metallic lithium that could lead to instabilities and compromise safety. Instead, a brief topping charge is provided to compensate for the small self-discharge the battery and its protective circuit consume. Depending on the battery, a topping charge may be repeated once every 20 days. Typically, the charge kicks in when the open terminal voltage drops to 4.05V/cell and turns off at a high 4.20V/cell. "
    Li-ion "Avoid full cycle because of wear. 80% depth-of-discharge recommended. Re- charge more often. Avoid full discharge. Low voltage may cut off safety circuit". "Loses capacity due to aging whether used or not."
    "If on the other hand, you use a desktop computer at work, and save a notebook for infrequent travel, Apple recommends charging and discharging its battery at least once per month".

    Oh, and just watch your Mac charging using System Profiler > Power. Its charge current behaves exactly as described in the Battery University article. After 5 hours or so charging stops and the battery floats. If you leave it floating on the charger for 24 hours you'll see the battery voltage drop a tiny amount. Exactly as described. I haven't had the patience to wait 500 hours to see if the topping charge is applied, but I'll bet it does.

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