There are many superstitions on what you must never do lest your battery become worthless - and by worthless I mean hold about 16 - 24 seconds of charge. This has happened to every laptop I have ever owned, and I just got a new one, so please help me sort out fact from fiction. Here are some of the things I've heard:

  • Do not keep your laptop fully charged. You must run it completely down every so often.
  • Do not use your laptop plugged in to the wall. Only plug it in when it needs charge.
  • If you will not be using your laptop for a long period of time, don't leave it at full charge.
  • Do not leave your laptop running 24/7.

The first two I know to be complete fiction: this was true of old batteries such as you might have had in an iPod in 2003, but modern batteries function better when kept at or near full charge. Devices even have circuitry to prevent you from completely depleting your battery, as this is dangerous.

The third point sounds probable, and I'd be interested to know if it was true. However, it doesn't really apply to me because I'm not really the type to leave my laptop alone for a day, much less a "long period of time"

The fourth seems most likely of the above, but only because of causality: I have always done this, and my batteries have always crapped out on me. I've generally treated a laptop like a desktop with a battery backup, and that I can move from one room to another if necessary. The fact that my batteries tend to last less than 30 seconds has further entrenched this behavior. Should I be trying to break this habit?

Are there any other things that ruin laptop batteries? I love that I can actually use my new laptop unplugged :) I'd like to keep it that way.

Update: Additional question: If the computer will be used for an extended period of time plugged in, does it make sense to remove the battery first?

Update 2: I know people with laptops older than mine, who actively use their laptops as much as I do, and their batteries still hold about an hours' charge while mine holds less than 30 seconds, hence my belief that something I'm doing kills them.

  • I tried a lot to find answers for this a while ago, and the only thing I learned for sure is that nobody is really sure. Answers will vary (though not necessarily contradict) and, in the end, you'll have to see which ones feel right. I, particularly, believe you shouldn't let the battery heat up too much, that just feels bad. :-)
    – Malabarba
    Dec 5, 2009 at 13:33

6 Answers 6


http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries has some useful information. It suggests the following tips regarding lithium-ion batteries:

  1. Don't fully discharge the battery (partial discharges are best)
  2. Don't heat up the battery when it's fully charged
  3. Ideal storage is about half charged in a cool environment.

Tip 2 would support the idea of not using a laptop while fully charged and plugged in, as laptops generate significant heat, and 3 would suggest against leaving a laptop in a car that's in the sun.

In the end I would think it's just simple degradation that renders batteries useless. There's only about 500 charge cycles on a lithium-ion battery before it becomes next to useless. Sure this improves as the technology matures, but I don't believe anything radical has changed since the linked article was updated.

  • What do you mean by "cycles"? I mean besides the obvious discharge/charge thing. I mean, If my battery is at 100% and I have it plugged in and on, it stays at 100%. Are cycles continuously happening? Or is the circuitry smart enough to bypass the battery entirely (i doubt this is the case)
    – Mala
    Dec 1, 2009 at 18:55
  • I don't know if it's used, but I know the technology exists to stop charging a battery once it's reached full charge - that's common in the AA and AAA chargers you find at radio shack and places. If the battery is fully charged and plugged in with the laptop on, I'd worry about keeping the battery hot while fully charged, but I'm not sure how that deteriorates the battery in comparison with a simple "cycle" Dec 1, 2009 at 19:14
  • 2
    A "cycle" is a full charge cycle from 0% to 100%. You don't have to do a full charge to achieve a cycle. You can do two charges from 50% to 100% and that counts as one full cycle. Wikipedia says Li-Ion batteries hold on about 1200 full cycles. Apr 17, 2010 at 7:47
  • The link is broken. Aug 13, 2016 at 9:17
  • @PeterMortensen I've updated the link. They rewrote the article with a lot more information! Aug 16, 2016 at 15:58

One of the best guides, covering pretty much any aspect of various battery types:

Battery University is an on-line resource that provides practical battery knowledge for engineers, educators, students and battery users alike. The papers address battery chemistries, best battery choices and ways to make your battery last longer.

As for your question, what kills laptop batteries:

  1. Heat, while the inside of a laptop may seem to be a cosy place (temperature-wise), it is certainly not the best environment for a rechargeable Li-ion battery.

  2. Age

  3. Charging and discharging, the number of charge/discharge cycles of Li-ion batteries are limited, depending on the quality of the battery, usually between 300 and 500.

  • 5
    +1 for mentioning Age. Batteries degrade just sitting on a shelf. So you can't buy a spare battery with your laptop and hope to use it when the original goes bad. (It may hold more charge than the many-times-cycled original, but not as much as the original did when it was new.)
    – stone
    Jan 19, 2010 at 7:47

I leave my laptop on 24/7 for weeks at a time, and after a year, I get around 1 1/2 hours of charge, so it has lost about half an hour.

I think it mainly comes down to the circuitry and how advanced it is. I know that my laptop keeps saying 95% charged and every 6 or so hours seems to cycle or do something - like discharge 5% here and there.

I think the main thing that kills them is simply complete charge/discharge cycles. At the end of the day, you get about fifty without seeing any affect, then I would say you loose a few seconds for each charge past that.

As you said, the first two are related to the memory effect which does not affect lithium-ion batteries.

Lastly, if you are using a battery pack that uses standard cells, you can replace them yourself if the manufacturer wants a fortune for a new one. A friend's laptop was getting about 3-4 minutes of charge and Sony wanted to charge £290 which is ridiculous as you are better off getting a new netbook for that! I opened it up and replaced with identical cells which costed around £25. For example, here is the inside of an Apple battery:

Alt text

  • Are any of today's lithium ion batteries built like that? Dec 1, 2009 at 18:38
  • Yes - those cells inside are lithium ion. Dec 1, 2009 at 18:46

Some newer laptops can be used without the battery installed, when plugged into the charger. Certainly my Dell Vostro can be used this way. If the battery is fully charged, and I'm running off mains - then I take the battery out. I've used it daily for 2.5 years now mostly with the battery out, but when I do use it, the battery still gives 4 hours.


First let's talk about "battery memory". Older batteries such as NiCads suffered from a memory effect; if you only discharged them to 75% then they would develop a "memory" and not work below 75%. Modern batteries do not suffer from this effect. You do not need to periodically discharge them.

Next batteries are composed of several "cells". If the voltage of the cell drops below too low, it could "reverse" it polarity. This puts it in opposition to the other cells in the battery and drastically reduces the batteries voltage. This also is seldom a problem today. Modern batteries incorporate "smart" circuits to prevent this.

Batteries are a chemical device. When charging, a chemical reaction stores the energy. When being used the chemical reaction is reversed, discharging the battery. There is always a small loss during this process. Batteries will eventually fail. The technology is getting better and they last longer, but they still do go bad.

I think we are more aware of this because we are keeping our laptops longer. It used to be that laptops were underpowered PCs that were quickly outdated. Today they are just a powerful as most desktops, and we can use them for several years before they become obsolete.


Here is a short guide on how to make it last/live longer: Battery Life saving tips.

  • 1
    That guide is information on how to make a given charge last as long as possible. I am asking how to stop the battery from deteriorating, i.e. stopping the amount of time used to empty a full charge from becoming shorter.
    – Mala
    Dec 1, 2009 at 18:18
  • if you leave it plugged in the battery gets very hot and that has a negative effect on the chemicals in the battery reducing there 'storging' capability thus leading to a shorter battery life this grows exponentialy with tempreture . This is one reason. The battery will deteriate over time there is nothing you can do about that(how longs depends on the type of battery).
    – Euclid
    Dec 1, 2009 at 18:38
  • @Euclid - every laptop on the market today will stop charging when your battery is fully charged. It should not get hot on its own. Dec 1, 2009 at 22:11

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