109

My friend told me that I need to disconnect the power cord when the battery is fully charged. Otherwise, I will shorten the life of the battery.

Other people say you should drain it once a month or point out that for long term storage, you should charge it to 50% and then periodically (3 to 6 months) bring it back to 50% and store it again.

I am going to use my laptop at home 90% of the time. So, I plan to have the power cord connected all the time.

I'd prefer to just plugging in my MacBook Pro and letting it be on charge long term and occasionally taking it away from the charger when I'm not at home or my desk.

Are these specific recommendations worth the inconvenience?

88

You do not need to disconnect your MacBook Pro's battery. Your battery will stop charging once it is full. Apple's modern batteries are much smarter than previous designs.

To get the most out of your MacBook Pro's battery, follow the Notebook Battery advice from Apple: unplug and use your battery until empty about once a month, then charge back up to full.

At the time of answering, Apple's advice read:

For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing.

If you need help following Apple's advice, use Battery Guardian; it is free and will remind you when to deplete your battery.

Battery Guardian helps track when the battery needs depleting

  • 4
    Your response seems contradictory to what is on the Apple Notebook battery site you linked to: "For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time." Are you suggesting that material is out-of-date? – codinguser Apr 18 '11 at 14:10
  • 13
    If you read the next sentence "An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge", the key words are "all the time". Don't treat it like a desktop. Periodically use it the laptop while unplugged. This is not the same a unplugging it every time the battery is full. – Anm Apr 18 '11 at 15:37
  • 2
    If you always keep your battery topped off, then it's almost as bad as long term storage when full. That decreases the capacity between 6 and 35% annually based on temperature (these numbers are for 0 C to 40C). Discharge cycles also wear down a battery - so it's safe in the short term, but not ideal in the long term. They are replaceable so if you prefer to have shorter life by always topping off - you can pay sooner for a replacement. – bmike Jun 10 '11 at 20:39
  • The Battery Guardian homepage, at the bottom, states: "Avoid leaving your laptop always connected to the power supply. This will shorten the life of your battery." This is a confusing endnote. – nute Jan 26 '15 at 9:27
  • 8
    Some MacBook owners never disconnect their computer from the mains power supply. They use the MacBook as if it were a desktop computer – always connected to the mains power and never using the portable capability of the device. At the time of answering, Apple's advice suggested that you disconnect and deplete your laptop at least once a month. That is, do not leave your laptop connected to the power supply permanently. – Graham Miln Jan 26 '15 at 11:00
55

No. The nature of the lithium battery chemistry does not require periodic cycling to maintain capacity.

Furthermore, the periodic cycling described in the apple documents listed above (@I-M-JM's Post) does not have an effect on the battery chemistry. It only serves to allow the battery capacity meter to accurately track the battery capacity.


Periodically draining the battery only serves to allow the Battery metering systems to accurately estimate the remaining battery capacity. It is not needed to maintain the battery itself, and actually wastes a battery cycle.

Basically, if you don't run your battery down for a long time, the next time you disconnect the laptop from AC, the estimated time remaining value will be incorrect. However, the actual battery capacity and runtime will be unchanged from normal.

The statement "For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally." from Apple's site is actually incorrect regarding the lithium battery chemistry at worst, and an oversimplification at best.


Furthermore, The battery metering and battery charging systems are separate, so inaccuracies in the battery metering system will not cause errors in charging the battery (before you ask). Lithium cells are actually quite simple to charge.

Ref:
http://en.wikipedia.org/wiki/Lithium-ion_battery
http://batteryuniversity.com/learn/article/lithium_based_batteries
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

  • 1
    Wow - I figured the long term storage implications of a full battery to be the same as always having it charged and topped up (and risk 20% permanent capacity loss annually). The new unibody batteries last so many more cycles I'm less concerned about duty cycles - perhaps the old data with simpler battery controllers is less relevant? – bmike May 17 '11 at 18:22
  • You get the 20% (or similar) capacity loss no matter what you do, as it is a function of breakdown of the battery chemically. There is a slight increase in capacity loss if you keep the battery charged all the time (most manufacturers actually recommend long-term storage at ~40% charge). However, either way, actually using the battery is worse then keeping it charged. – Fake Name May 18 '11 at 0:59
  • 3
    Thanks - I saw table 3 of batteryuniversity.com/learn/article/… and was amazed that they quote only 4% annual loss if the battery is at 40% charge instead of 20 % annual loss 100% charge at 25C. Makes sense why service batteries are usually 50% or less. – bmike May 18 '11 at 3:16
7

I keep my macbook pro plugged in all the time with no adverse effects. And if you want to use your mac laptop in clam-shell mode (ie lid closed, connected to an external monitor), then you will need the power supply plugged in anyway.

Still, I (and Apple) recommend to unplug it every month or so and use the battery a bit, just to remind it that its a battery ;) Keeps it healthy.

4

From Apple's Notebook battery site (emphasis mine):

For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing.

3

I would suggest that you read following 2 articles:

  1. http://www.apple.com/batteries/
  2. http://www.apple.com/batteries/notebooks.html

From my personal experience, don't charge fully, and you can disconnect it after you charge till 90% or more.

2

I use Watts which tells me the current state of my battery (in terms of total capacity) and has a regular calibration process to improve its lifetime. It costs $6.95.

1

I'm adding my personal experience here that I recently had with my MacBook Pro 2015 15" (maxed out options).

I've always kept it on the charger because I always use it docked-in both at home and at the office. Per my system information, I have only 198 cycles on the battery (again, original battery since 2015).

Last week my case had swollen up completely... turns out all the lithium cells became defective. I took it to Apple and they pretty much said that I'm responsible for the battery going bad and that I had to pay for the parts and replacement.

tl;dr: 2015 MBP has less than 200 cycles as I always kept it on the power cable, but that per-apple damaged the batteries and I'm now responsible to cover all costs to repair.

1

Don't worry about it and just use your MacBook Pros for what you bought them for.

Why?

Physics. No matter what you do, you can't change the laws of physics and lithium batteries are governed by age and the number of charge cycles. A complete discharge and recharge is one cycle. A 20% discharge 5 times over is one cycle, a 5% discharge 20 types is also one cycle.

Whether that cycle takes a half day, a full day or a week all depends on how you use it; but I am guessing you didn't buy a MBP to sit on a shelf all day long doing nothing.

Even when you keep your MBP plugged in, you are reducing the per day cycle count; however you are not eliminating it. But the bigger question is, did you buy a MBP to sit at a desk all day? If so, you should have bought an iMac instead - there's no battery so you eliminate this problem altogether.

That said, there are things you can avoid that will shorten the life of your battery and those things include:

  • Extreme temperatures - high heat and freezing temps can kill a battery prematurely.
  • Drops and physical stress can damage the battery shortening its life

  • Not using the right charger can harm your battery. Always use a GENUINE power adapter, not some discount charger you find on eBay.

When they do die, it's always best to get a good quality replacement battery from a reputable manufacturer. The 2006 MBP uses an external battery so it's fairly easy to find replacements - and some even come with generous warranties.

The 2013 MBP Retina (and newer) batteries require the back cover to be removed, but are actually pretty easy to replace even though they may be glued to the top cover. You can find many good replacements now on the aftermarket, with generous warranties as well.

When you get down to it, the battery prices are not that all off putting.

The bottom line is that you batteries have a life span that's governed by age and use and there is nothing you can do short of not using your MacBook to change that. But...that kind of defeats the purpose of having the MacBook in the first place.

0

Get authoritative information whether your battery is fully charged or is it still charging by following these steps:

  • Go to About this Mac
  • Click on System Reports
  • Click on Power. Observe "Charge Information"
  • Why do you even bother? – atilkan Nov 15 '18 at 13:05

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