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Should laptops remain plugged in when their battery is 100% charged?
What is it that kills laptop batteries?

Because of convenience, I had to move my laptop to another room away from room where I always ran laptop on UPS without using battery. UPS is specifically there for protection from surges and power outages. Since so far I always run laptop on battery, I question the proper usage to prolong battery life.

Currently I run laptop on battery with power supply so battery is constantly being charged until it is full 100% and when it is, I disconnect power supply and continue working until battery meter shows 10% remaining. That's when I plug in power supply and let it charge until 100% once again while I work. But it takes a lot of time to fully charge laptop while working since my power supply is 60W which should be the reason of such slow charge and I think the kind of charger that I use is express charger.

The thought of charging laptop until full, all while doing my work makes me think that if it takes way more time to charge, it might keep battery running warm for the period of charging time which brings me to question about whether I should keep running laptop as I've described above or it would be better to leave power supply constantly connected to laptop to keep battery between 99%-100%? On one hand it won't keep battery warm but it will try to frequently supply charge to battery once it gets 99% to replenish charge to 100% (which might reduce battery life?). On the other hand if I'll keep working solely on battery and recharge it when below 10%, the battery will get warm but only when charged.

Can anybody suggest the correct way of running laptop on battery to ensure better battery life? Also, since keeping my laptop in good condition is important to me, I no longer leave it plugged in mains without battery and since UPS served me as backup in power outages and surge protector, I now rely on my battery to substitute UPS, at least in means of a backup in power outages.

Dell Latitude E6420
Windows 7 64-bit


If you examine the typical usage, or expected usage scenario, you actually can determine the general protocol for how to treat your battery.

In general, a laptop owner will plug in their laptop if they are near an outlet, and use it while it is connected to a wall outlet for the duration of their session. They do not want to be bothered with removing their battery, or connecting/disconnecting from the wall outlet at regular intervals. In more extreme cases, if a laptop battery has ever proven to have an issue with this type of usage (getting excessively hot and/or exploding while the laptop was plugged in) it was recalled as being defective. So, this tells you first of all, that allowing the battery to maintain a full charge for an unlimited amount of time is not a bad thing for maintaining a healthy battery.

We move on to looking at general laptop usage off a power grid. Most people actually don't open their laptop and in a single session drain their battery until the laptop shuts off. Most people actually use their laptop on the battery for a few minutes, and then turn it off. They will use it a few more times for sessions of varying length, get the warning that the battery is low, and then plug it in to charge. This is not to say that some people don't use their laptops in a single session until that warning. Of course some do. Just that most don't. Almost everyone will see that warning of a low battery... a 15% to 5% remaining charge left warning before they seek a power outlet. Which means that a large number of laptop users... one could say a Majority of laptop users will use their laptops on battery until it is drained before they charge it again.

Here is what most people miss. It's not so much the temperature of the battery that will reduce it's life. It is the number of charge cycles. The more times the battery is charged, the shorter the amount of time it will provide a full charge for. By charge cycles, I don't mean the number of times it has received a micro-charge... sitting there topping off constantly. I mean, the number of times it has been drained significantly, and then recharged.

For example. I have a 2004 Toshiba Satellite A75 that is a power hungry monster (120 watt adapter). Two fans, 3.33ghz P4 HT processor. So, with the battery that came with the unit, I would see around 2 to 2.5 hours of usability on the battery when new. I still have the original battery, and I can get just under 2 hours of use out of it. Why, after 8 years does this battery still function relatively well? Because the laptop BARELY ever gets used on the battery. The battery sits in the laptop, and the laptop sits on the counter plugged in all the time.

If you have an actual UPS.. a battery backup system, it will retain the ability to run a system on battery for a longer period of time if you don't actually end up using it.... as opposed to if you have to use it every week due to power outages. If you have a home alarm system that has a battery to maintain it, that battery will last 4-5 years if you don't have frequent power outages, but might only last 2 years if you have a large number of storms that kill power for hours at a time. It's all about the charge cycles.

If you want to extend the battery life... meaning if you want to avoid having to go out and purchase a new battery, then actually not using the battery is the way to go. Leaving it in the laptop and just not using it on battery power will give you the longest usability life span possible. That's not entirely feasible though if you want or need to use the laptop on battery power.

Here is a suggestion. Purchase a second battery, and purchase an external battery charger like this one. Why? Depending on the external battery charger, it will either spend less time charging while on the external charger (which will mean it will be getting warmer for a shorter period of time) or if it is a trickle-type charger, it won't get as warm while charging. Then, you can use the second battery while you are charging the first. Should you be concerned with the temperature of the battery while it is charging? No. But, this solution would alleviate those concerns.

Otherwise, just use the laptop as you have described.

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  • Thanks! So you suggest running on external power while having battery inside? Maybe there is constant charged level I should maintain i.e instead of 99%-100% should keep it between 40%-80%? – Boris_yo Sep 2 '12 at 16:47

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