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Is it better to use laptop on battery or on AC power?

I bought a new laptop (a Sony Vaio) and I am used to working on it while the power adapter is connected.

Now that the battery is full on this new laptop...
What is the recommendation regarding this?

Should I either disconnect the power cable once the battery is full or let it plugged in while working?

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marked as duplicate by Arjan, Diago Sep 5 '10 at 9:18


Could you please rephrase your question? I have really big problems understanding you. –  AndrejaKo Sep 4 '10 at 17:17
Clarified his question based on the last sentence, tried to do minimal changes. –  Tom Wijsman Sep 4 '10 at 17:24
Can somebody tell me why this question got 3 votes? –  rabidmachine9 Sep 4 '10 at 19:14

5 Answers 5

up vote 4 down vote accepted

If you are asking if you should disconnect your computer from power once the battery if full, the answer is no. If you do so, your battery will keep discharging and charging. The number of times batteries can be charges is limited and if you unplug your computer every time it is full, it will quickly die.

If computer is in such location that it will be almost always connected to power, it may be smart to disconnect it once every two weeks or so and let it run on batteries for a few minutes.

Also, since the laptop is new, it probably uses lithium based batteries. That means that you should avoid completely discharging the batteries because doing so will considerably reduce their lifetime (on older nickel-metal hydride batteries, opposite was true, but they aren't used in laptops any more).

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While you are true in that li-ion CELLS can fail if allowed to discharge too much, in your laptop you have a battery, a collection of cells. This allows for enough voltage and sufficient power to be stored. It also allows the battery to manage it self. it will stop providing any power at all once it reaches a level too low for it to be OK for the battery, it also prevents the cells from being over charged, and unless you have a really cheap laptop, should monitor the heat to prevent death by laptop. li-ion cells them selves are fine be charged little bits here and there, and last about 3 years –  thecoshman Sep 6 '10 at 10:11
@thecoshman Li-ion batteries die when discharged. Fortunately they have electronics which prevent the discharge, just like you said. What I was pointing out is that their wear is not linear function. If you discharge battery to 40% of full charge and charged to 100%, the loss of capacity will be lower than if you discharge to 10% and then charge it to 100%. –  AndrejaKo Sep 6 '10 at 10:56

I would always leave a laptop plugged in whenever I can.

Many modern machines have power save modes and/or can underclock the CPU when on battery power so you will get reduced performance if unplugged. (Although it usually is configurable, but why bother).

Also, batteries only have a finite life, therefore whilst it is good practice to do a complete charge/discharge cycle at least once every so often, the more times you run the battery down from start to finish - the less total capacity you will have.

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From what I have learned reading magazines and also from my personal experience using two different laptops during the last 6 years: If you want to save your (Li-Ion)-battery and keep it as fresh as possible, the best way would be, to take it out of the laptop if the charge is down to about 35-40% and only run your machine with cable. I also tried not to charge or discharge the battery completely. If possible, I tried to charge the battery while the laptop was turned off (or used the docking stations extra power to charge it). Doing so, I did not have to change the battery after 2 years - like most of my colleagues with the same machines were forced to.

Disadvantages are comfort related: You need to know, when you need your battery - it has to be charged 1-2 hours before you take your laptop off the power plug. Other than that, on a sudden power loss, your laptop has no buffer and therefore will turn off.

For my new laptop, I decided, to set the threshhold for battery charging via boot script, so that it will never charge completely and is mainly kept between 40 and 70%. I have an extra button, that will trigger a complete charge of the battery on my desktop. But I basically decided, that the disadvantages in comfort are not worth an extra year or two with my battery.

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When my battery is fully charged and I'm not going to be moving for a while I actually take it out of the laptop with the laptop still plugged in. You can't be hurting the battery if it's not in there (unless you don't use it for months).

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Actually, you can. Modern batteries will have problems if they are stored under certain charge levels. From what I learned from various websites, it's safest to charge the battery then let it discharge to between 40% and 50% and then take it out. this way it should suffer the least amount of damage from storage. –  AndrejaKo Sep 4 '10 at 18:07
I gave you +1 for that comment, although he did state "unless you use it for months". –  pattern86 Sep 4 '10 at 19:02
On Apple notebooks, you should not take out the battery, and that might very well apply to other brands as well. (And, as a bonus, this also avoid loosing data when you accidentally trip the wire.) –  Arjan Sep 4 '10 at 19:09
@Arjan I'm glad I didn't buy any Apple laptops! Reading that article made me question Apple's engineering practices. One of the mot important rules should be that power supply should be strong enough to provide power for computer under full load and to charge battery at the same time. I'm really disappointed in Apple right now. –  AndrejaKo Sep 6 '10 at 11:00
@AndrejaKo, but it does result in small power supplies. That's a great advantage to me! –  Arjan Sep 6 '10 at 19:14

After so many dead batteries or those that only hold a charge for 30 mins or less, I have started unplugging my laptops and netbooks once they are fully charged. This has produced a lot better result than leaving them plugged in. I have found that especially in the case of Apple devices this can make the difference in having a usable MacBook Pro and one that must stay plugged in at all times. Lastly, some of the recent VAIO's have had their batteries recalled so you may want to see if you're on the list.

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I don't get it. While charged and plugged in, a MacBook battery should only be used for peak power. Hence, I don't see how leaving it plugged in is much different from shutting down your computer. –  Arjan Sep 4 '10 at 19:11
I would think it should work that way but I have a macbook pro that would display otherwise. I might be seen as a fluke by fanboys but it also occurred at work on one of the graphic designers laptops; also a macbook pro (purchased about a year after mine) –  Mondain Sep 4 '10 at 23:30
