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Is it safe to charge my macbook after the green light shows? Would it not overcharge the battery, or reduce its lifespan?

I've heard that doing this is completely safe and it increases the cycles or something. Is that correct?

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Yes, leaving the charger in will not hurt the battery in the short term. However, you should occasionally allow the battery to be used and not leave it plugged in all the time. The battery works best when it is cycled; Apple has a brief writeup on their use of Lithium Ion batteries in the MacBook line at http://www.apple.com/batteries/why-lithium-ion/, where they state that a complete charge cycle (not the same as charging to 100%) is what will tend to reduce the capacity. A charge cycle can be adding 10% to the battery each day for 10 days, adding 100% of a charge in one day, or anything in between.

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  • Okay so u r very sure nothing will happen if i let it on the charge once in while (overcharge it)? im sorry im being so pranoid lol – user175467 Mar 16 '16 at 15:20
  • Yes. I've done it every day with my MBPr for the past year when I put it in my LandingZone Dock -- it charges for a couple hours, then is green the rest of the day. I take the MBPr home every night and use it on battery for anyplace from 30 minutes to 8+ hours over the weekend, without negative effect. The thing to remember is to use the battery, and not leave it plugged in 100% of the time for weeks or months -- the battery was made to be used, so feel free to use it! – Alphaman Mar 16 '16 at 15:33
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Is it safe to leave in? Yes. To understand this better we need to know what is happening when you have your charger plugged in.

What do the LED's on the MagSafe Charger Mean?

Amber: Battery is charging.
Green: Battery is fully fully charged and no power is being sent to the battery.

Your battery will naturally dissipate it's charge without use and the charger will detect this drop and automatically begin its recharge cycle.

Is it safe?

I am assuming you are referring to the longevity of the battery and not whether you will incur some sort of injury.

What affects the life of a battery are two things:

  1. Number of Cycles - how many times the battery has been discharged and recharged. 1 cycle is a 100% discharge and recharge, or 5 20% discharges and recharges or 100 1% discharges and recharges.
  2. Age - this is actually the number one reason for batteries to fail. Basically, a 3 year old battery that has never been used is going to perform about as well as a 3 year old battery that is used every day.

I answered a similar question recently about What's the best way to prolong the lifespan of a MacBook Pro battery?

Catalina Battery Health Management Feature

As of Catalina (10.15.5), there is a new feature; it's called Battery Health Management. It will actually stop charging your battery and lower the maximum charge amount further making the micromanagement of your battery unnecessary. See the linked post for further details.

Leaving it plugged in will surely have pretty much zero effect on your battery.

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