2 Replies Latest reply: Feb 28, 2014 10:32 AM by PlotinusVeritas
priyesh0904 Level 1 (0 points)


I have some questions regarding battery and charging-

When the battery is 100% charged and the light on the charger pin turns green is it safe to keep the macbook plugged in or should i remove the charger. Most people will think that this is a dumb question but here is my reason. If you keep the charger plugged in even after the battery is 100% and click on the battery icon on top it says power source is ac adapter. So does this mean that their is no situation of overcharging as the power from the charger is now being used to run the computer rather than overcharging the battery?

Also if I keep charging and discharging again and again will it not shorten the battery life faster? because usually the more charging/discharging cycles you have the sooner the battery starts to lose its capacity.

I have had the macbook air 2013 for around 15 days now and the total number of charging cycles are 18. Usually after around 500 cycles the battery capacity starts to decline( I dont know this for a fact but it comes from a good source)

Thoughts/suggestions please.

Thanks in advance

MacBook Air
  • actionmarker Level 4 (1,505 points)

    You cannot overcharge the battery by leaving the charger connected.

    Once the charger turns green, the charging current reduced. The battery charge will be allowed to drop to approx. 95%, before the charger 'kicks' in again, topping it back up to 100%.


    It is however good to cycle the battery through a full charge to maintain optimum battery performance. I do this about once per week


    Have a look at this page for further information




  • PlotinusVeritas Level 6 (14,720 points)

    priyesh0904 wrote:


    Also if I keep charging and discharging again and again will it not shorten the battery life faster? because usually the more charging/discharging cycles you have the sooner the battery starts to lose its capacity.



    Charging cycles dont really matter except in very long term "old age" of the battery.


    what matters is short term treatment.


    Cycles arent what is prematurely killing a battery, rather harsh treatment / use  (see below).





    General consideration of your MacBook battery

    Contrary to popular myths about notebook batteries, there is protection circuitry in your Macbook and therefore you cannot ‘overcharge’ your notebook when plugged in and already fully charged.

    However if you do not plan on using your notebook for several hours, turn it off (plugged in or otherwise), since you do not want your Macbook ‘both always plugged in and in sleep mode’.

    A lot of battery experts call the use of Lithium-Ion cells the "80% Rule", meaning use 80% of the full charge or so, then recharge them for longer overall life. The only quantified damage done in the use of Lithium Ion batteries are instances where the internal notebook battery is “often drained very low”, this is bad general use of your notebook battery.

    A person who has, for example, 300 charge cycles on their battery and is recharging at say 40% remaining of a 100% charge has a better battery condition state than, say, another person who has 300 charge cycles on their battery and is recharging at say 10-15% remaining on a 100% charge. DoD (depth of discharge) is much more important on the wear and tear on your Macbook’s battery than the count of charge cycles. There is no set “mile” or wear from a charge cycle in specific. Frequent high depth of discharge rates (draining the battery very low) on a Lithium battery will hasten the lowering of maximum battery capacity.


    All batteries in any device are a consumable meant to be replaced eventually after much time, even under perfect use conditions.



    If the massive amount of data that exists on lithium batteries were to be condensed into a simplex, helpful, and memorable bit of information it would be:


    1. While realistically a bit impractical during normal everyday use, a lithium battery's longevity and its chemistry's health is most happy swinging back and forth between 20% and 85% charge roughly.


    2. Do not purposefully drain your battery very low (10% and less), and do not keep them charged often or always high (100%).


    3. Lithium batteries do not like the following:

    A: Deep discharges, as meaning roughly 10% or less on a frequent basis.

    B: Rapid discharges as referring to energy intensive gaming on battery on a frequent basis (in which case while gaming, if possible, do same on power rather than battery). This is a minor consideration.

    C: Constant inflation, as meaning always or most often on charge, and certainly not both in sleep mode and on charge always or often.


    From Apple on batteries:



    "Apple does not recommend leaving your portable plugged in all the time."




    In a lithium battery, deep discharges alter the chemistry of the anode to take up lithium ions and slowly damages the batteries capacity for the cathode to transport lithium ions to the anode when charging, thereby reducing max charge levels in mAh. In short, radical swings of power to lithium cells disrupts the chemical ecosystem of the battery to hold charges correctly which likewise impedes the perfect transfer of lithium ions both in charging and discharging.  In charging your lithium battery, lithium ions are “pushed uphill” (hard) to the anode, and discharged “downhill” (easy) to the cathode when on battery power. Deep discharges, damages this “upward” electrolyte chemistry for the battery to maintain a healthy charge and discharge balance relative to its age and cycles.


    Optimally, in terms of a healthy lithium battery and its condition, it is most happy at 50% between extremes, which is why low-power-drain processors such as the Haswell are ideal on lithium battery health since a partially charged battery with a low-drain processor has, in general, much more usage in hours



    There is no calibration of current Apple portable Macbooks with built-in batteries.



    There is no battery calibration with current Apple portable Macbooks with built-in batteries. Lithium batteries have essentially a 0-‘memory’, and all such calibration involve the estimations fed to the system controller on the SOC (state of charge) of the battery over long periods of time as the battery degrades. The software based battery controller knows the battery's characteristics, or SOC and adjusts itself. This is why there is both no need and purpose to periodically deeply drain your macbook battery, since it doesn’t affect the characteristics of the battery, and further still deep discharges are something you should not do on purpose to any lithium battery.



    From BASF: How Lithium Batteries work