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When I'm at home, is it better to use the laptop plugged into AC power, or with just the battery, for the overall battery life?

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9 Answers 9

up vote 76 down vote accepted

It won't make all that much difference. What will shorten battery life is temperature: If it gets hot, it will shorten the battery life. Best thing to do, if you are able, is to remove the battery while you're at home and keep it somewhere cool.

If it's a Li-ion battery, then they don't like to be completely discharged, so make sure you charge them regularly. Wikipedia:

Lithium-ion batteries should not be frequently discharged fully and recharged ("deep-cycled"), but this may be necessary after about every 30th recharge to recalibrate any electronic charge monitor (e.g. a battery meter). This allows the monitoring electronics to more accurately estimate battery charge.[26] This has nothing to do with the memory effect.

More tips can be found here:

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Indeed. Contrary to what most people think, the power circuitry is usually smart enough not to charge the battery after a threshold. The primary issue is temperature. –  LeakyCode Jul 24 '09 at 17:31
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Apple MacBooks actually run slower when you unplug the battery, as the A/C adaptor cannot provide all peeks that may occur in power usage. I guess this may be true for other brands as well, so even though it may increase battery life, I'd not recommend to take the battery out. See tomshardware.com/news/… and Apple's support.apple.com/kb/HT2332 –  Arjan Jul 24 '09 at 17:46
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I read somewhere that removing the battery while on AC power might leave the laptop vulnerable to damage from power oscilations. Is there any sense to that? –  Bruce Connor Oct 9 '09 at 4:36
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@Mehrdad - Temperature and keeping them fully charged shorten their life. Now find a laptop that doesn't cook its battery while running. @Arjan - Windows default power settings are generally to conserve more power at the expense of performance when running on battery. However, if AC power is connected then the battery is not needed, after all, the PSU can supply enough power to charge the battery AND run the laptop. @Bruce - no more so than any other PC. They use a switchmode PSU which are normally fairly resilient to crappy power. –  pipTheGeek Sep 6 '10 at 11:38
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Make sure you tell the laptop to hibernate or standby after x time, if on battery. that's v important, or one day, the power cord may come lose and you won't know and you come back and find your laptop off. Or you just left it on battery by mistake and it went off.. I suppose you don't want to do that to the battery.. (unless it's new and you're cycling it as per instructions the battery came with) –  barlop Apr 10 '11 at 12:31

Apple has a good page on lithium ion batteries which should apply across the board to other manufacturers, not just Apple. Basically, keep your device (laptop, phone, etc) plugged in whenever possible. When the battery is discharged to around 70-80%, recharging will be another cycle, and batteries only have so many cycles before they need to be replaced.

It is good for the battery to be completely discharged every so often, about once a month.

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I really don't understand Apple's idea of cycles. I doubt the battery will be affected by whatever the chip on the battery thinks is a cycle... Or is Apple trying to say that the way of charging is really different when it gets to another cycle? –  Arjan Oct 10 '09 at 13:49
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Lithium Ion batteries have a lifecycle measured in # of "full" charge cycles. Each full cycle reduces the total charge the battery can hold by a miniscule amount. A full cycle isn't the same thing as a full discharge and recharge (though that does count as a full cycle and is bad for lithium ion batteries to do often). A full cycle is counted as each time an amount of charge equal to the capacity of the battery is used up - in other words, if you use 10% and then charge and do that 10 times, that's a full cycle and is roughly equivalent to a full discharge (though not bad for the battery) –  ScottCher Feb 1 '11 at 13:20
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@Arjan its not the chip tracking the number of full charge cycles, its the physics of the way the battery works. Lithium Ion batteries see a reduction in the charge capacity each time they go through a full cycle. Think of it like carbon paper - each time you use it, its ability to create another copy of something is reduced and the quality of the copy is lower. –  ScottCher Feb 1 '11 at 13:23
    
If I'm not mistaken, most Apple devices don't even allow the user to remove the battery. What kind of answer would you expect from Apple then? –  Aeronth Jul 11 '13 at 14:21

A lot of people seem to be still giving information about old technologies. for the last few years more or less every device with a (semi) integrated battery will be using li-ion. Devices like hand drills use Ni-MH (usually) as they can provide high current, but they are prone to 'memory effect' this is basically the cells not losing the full capacity and is caused by charging the battery here and there, a bit at a time. These USED to be used for laptops as well, so it would have been better to fully discharge your laptop, then let it fully charge up.

A non-utter crap laptop would then notice that the battery was fully charged, and stop trying to charge it and just run of the mains anyway.

Like I said, Li-ion is the technology that is used today, better in more or less every way except it can't provide high current like other batteries (think car lead acid batteries) but this is not an issue for laptops. A basic Li-ion CELL (cell being the key) is a bit dodgy, if you short them or try to draw too much current they can over heat and explode. if they get too hot, they can explode. if they get discharged too much, they can stop working and you will not be able to charge them.

NOTE THAT I AM TALKING ABOUT CELLS THERE!

In your laptop you have a smart battery. It manages the power for you. It stops charging the cells when they are full, and stops giving power when they are too low. Prevents them getting shorted or having too much current drawn from them. The best thing about Li-ion cells though is that you can just top them up here and there, giving them a bit of power every so often, a full charge. They do how ever have a life time of about two or three years (last I checked anyway) and thus eventually lose their max charge (read time you can run of the battery for).

One key thing to consider (depending on where you live) is power cuts, if you computer suddenly lose AC power, it is not healthy. The same for your laptop, if you have removed the battery. The battery works like a UPS (uninterruptable power supply) so you can still use your laptop and turn it off safely.

erm.. hope that helps, bit long winded :P

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I'd keep it plugged in. Some laptops have a threshold where the AC doesn't charge the battery at all until it drops below a certain point. I've also read that you extend battery life if you maintain a charge of around 35%.

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Actually the lower its charge level, the longer it will last. Assuming a constant temperature. However, laptop batteries will have some electronics in them to monitor the health of the battery, these electronics are a constant (although very small) drain on the battery. If you let it get too low then the electronics will prevent the battery from being changed because of the risk of fire. –  pipTheGeek Sep 6 '10 at 11:41
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Fire as a result of low voltage? –  Boris_yo Sep 2 '12 at 16:36

In my experience running on battery means the screen brightness is reduced, I'm assuming to save power. So I prefer to keep it plugged in to mains power so I get the full brightness of the screen. If the laptop doesn't live as long then so be it, I'd rather not strain my eyes. As to bettery life I run mine down every so often but generally try to keep it near fully charged and connected to mains when I can. Additionally I try to raise the four corners of it by a few cms to improve the air flow and therefore cooling underneath it. However I think most of the heat is being generated by the CPU working hard and not the battery

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-1 for not answering the question. SU is not a forum. :) –  William C Feb 24 '12 at 22:44
    
@William C - I disagree I answered the question just not directly. Better to keep it plugged in - yes because of brightness. No - because of heat , but how I counteract the heat –  ianfuture Mar 15 '12 at 19:08

Also, you should never store the battery completely discharged. This can really reduce its life. If you are storing it for a long period of time you should keep it around 40% and somewhere cool.

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It's better to unplug the battery and be plugged into AC power, but be sure sometimes to do the complete cycle of the battery (from full charge to totally empty)

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6  
Apple MacBooks actually run slower when you unplug the battery, as the A/C adaptor cannot provide all peeks that may occur in power usage. I guess this may be true for other brands as well, so I'd not recommend to take the battery out. See tomshardware.com/news/… and Apple's support.apple.com/kb/HT2332 –  Arjan Jul 24 '09 at 17:43
    
Well, we learn everyday. Thanks :) –  Yoann Le Touche Jul 24 '09 at 17:50
    
If it's a Li-Ion battery (most are nowadays), you should try to aviod running it completely flat. en.wikipedia.org/wiki/… –  ThatGraemeGuy Oct 10 '09 at 12:42
    
Unplugging the battery is a bad idea, especially if you trip the MagSafe connector, then it skips Safe Sleep and goes straight into Hibernate. And it's inconvenient. –  Jared Updike Oct 22 '09 at 19:21
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@Jared: Actually, if the battery is unplugged and the MagSafe connector as well, won't the laptop just switch off? After all there's no power left... –  sleske Jul 28 '10 at 22:26

You can use both ways on AC or Battery there are some factors you should consider:

  • Proper Charging and Discharging

  • Environment Temperature

  • and for complete details on battery life check this link

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When playing games, protect your batter from heat and remove the battery from your PC.

Clean the cooler and its holes regularly. Use a compressor to push the dust in (or blow, but close your eyes and dont breate in) and the fan throws the dust out at you.that's how you clean laptops.

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