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I have an early 2011 13" MacBook Pro and I use it almost like a desktop. I leave the power cord connected all the time. Is this OK? Am I ruining the computer or diminishing its lifespan?

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4 Answers 4

up vote 7 down vote accepted

All Macs cease charging and let you know this by changing the "orange" LED in the charging cable to "green" when the battery is topped off and you are merely running the Mac - not charging it.

The question you ask would be more precisely worded - what harm is it in keeping the battery constantly and always topped off to full?


Your early 2011 13" MacBook Pro has a lithium ion battery. Luckily, lithium ion batteries have an internal circuit to prevent the battery from being charged over 100%. There is a very slight chance that something can go wrong with the charging mechanism in the laptop, which would cause the battery to overcharge, but I wouldn't be concerned with that.

Years back, laptop batteries were made from nickel-cadmium or nickel metal hydride. It was recommended that these batteries were regularly fully discharged then fully charged so they'd continue to hold a full charge, though even following these practices they would eventually lose capacity.

Apple still recommends that you fully discharge your battery monthly, and never store your laptop with a charge below 50% for an extended period of time. In short, it's perfectly acceptable to leave your laptop plugged in while it's in use but let it fully discharge once a month for optimal battery health.

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There are mixed opinions about this. Some say it'll shorten the battery's lifespan, others say the intelligent charging circuitry will prevent that from happening. I've always discharged the battery totally at least once a month as per Apple's guidelines. You can also see they do not recommend leaving it charged in all the time. Even their own guidelines aren't clear.

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This advice is spot on for the overcharging issue - the design of the charge circuitry only engages when the battery needs a charge. The implications of never draining a battery and keeping it "stored" at 100% charge does take some life off the battery. Whether it's better to use it too much or not enough - the guidelines are clear - discharge it normally to "0%" in the menu bar monthly to improve the length in months the battery remains vital. –  bmike Apr 30 '12 at 20:40

Here's my insights from eight years of laptop using experience.

The laptops that I've mainly used as a desktop (and left plugged in for the majority of the time) have all had their batteries lose a considerable amount of charge capacity within one year. A couple of batteries lost 80% of their charge just past a year of use.

When I've used them more on-the-go, I saw no giant reductions in charge capacity over a two year span.

I now try to fully discharge the battery at least once per month. Six months with a late 2011 MBP 15", and I see no difference in capacity.

So, my history indicates two points:

  • fully discharging the battery will help to some degree
  • batteries and charge controllers are better now than 5 years ago
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I would echo everything said here with one caveat that the new unibody macs have much smarter charging and longevity designed into them. Whereas pre-unibody batteries would always show signs of reduced full charge capacity between 300 and 400 charge cycles, now it's a rare circumstance when a battery doesn't achieve the same degradation until 4 years of being always topped off. The days of needing a new battery after a year of hard use or two sitting full seem unlikely to return to Macs with batteries. –  bmike May 2 '12 at 16:34

As an AAST for close to 20 years, I recommend to my clients to leave the computer connected to the power adapter and only use on the battery when necessary but being sure to cycle the battery once every 2-3 weeks (for Lithium Ion batteries. I also recommend using the Reminders app or the Calendar app to setup a recurring reminder to cycle the battery.

The life of the battery is determined by the combination of charge cycles and full charge capacity (FCC) against specification. You will not find the FCC specification publicly. You can take your computer into an Apple Retail store (be sure to make an appointment) to have a diagnostic run that will provide you the results. This information is important as it relates to the warranty you have remaining on the entire computer. If your battery falls below 80% FCC but is under the break point for cycles, (device specific) the battery will be covered under your warranty as a bad battery. If the battery exceeds the cycle count by even one, the battery will be considered consumed and you will have to pay for a new one regardless of warranty status and the FCC.

The current generation of Apple portables have cycle counts that exceed 700, so the chances of your battery becoming consumed before your warranty (either limited or extended) expires will be very low using the aforementioned approach.

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