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Aesthetic_Mess's avatar

How often should you let your laptop run on battery power alone?

Asked by Aesthetic_Mess (7858 points ) October 21st, 2010

I let mine run on it till it’s dead, or about 7% left, then I charge it, and let it run again til it’s 7%. Is that good? Or should I switch to plug power more often?

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2 Answers

camertron's avatar

There are all kinds of schools of thought on this one. I have heard the same as you have – that it’s healthier for a battery to be completely run down, then charged to full power. I have noticed that the batteries I have had in laptops have lasted a shorter amount of time when I have them plugged in all the time. In reality though, a battery is going to die sometime anyway, so you might as well do with it what you will and buy a new one when it won’t hold much of a charge anymore. The difference in the amount of time the battery will be usable is negligible.

LuckyGuy's avatar

Great question. You might save some batteries from going to the landfill.

There are three factors in play here.
First: All rechargeable batteries have a limited useful life measured in Life Amp Hours (not to be confused with the working or storage Amp Hours that is stamped on the battery). Lithium Ion batteries have Life Amp hours that are typically 300x the working value. That means theoretically you should get 300 full charges and discharges out of your battery before you need to throw it out. Look at your cell phone. If you charge it every day the battery will last less than a year. If you charge it every other day or when it needs it, the battery will last for years. So, according to this first factor, . if you are only concerned with life, it is best to run the PC from the wall plug all the time.

Now here’s the second factor: All batteries (even though some say they do not) take a set. If you keep it charged all the time it will eventually loose the capacity for deep discharge and charge. So, to optimize for this factor you want to let the battery run down and fully charge it as often as possible.

The optimum is somewhere in the middle. If you can plug the laptop in, do so. If you can’t then run on battery. Try to let the battery run down in normal use about 1 time every 2 weeks or so. It does not make sense to run it down just to empty it. You are wasting one of your life cycles. Depending upon your PC, there is a battery state of charge algorithm that learns the battery and usage and adjusts itself as the battery ages. Let it work.

The third factor is heat. Heat is the nemesis of batteries and electronics. You want good air flow around the pc at all times. Prop up the rear end on a book to allow heat to escape. Keep the vents open. Do not sit your pc on your bed covers while running it. The heat can’t get out. Place it on a clip board if you have to use it on your lap. I know it feels warm and toasty in the winter but that is not good for you or the battery.

Follow these rules and your PC battery will last for at least 5 years.

Hopefully we just saved a battery or two from the landfill.

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