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sleepdoc's avatar

Help me understand laptop battery life (details in question)

Asked by sleepdoc (4690points) July 15th, 2010

It has been explained to me that you should always let the battery run completely down before charging it. I understand this in concept. Where I get confused is using my laptop with the power cord. So if I am at a desk and I can plug in the computer, does this somehow impact the battery life? An example, I plug the computer in and start if up. Now I have to use in but have to disconnect it from the power cord. Should I then run on battery until the battery is out before I plug it back in even if I am going to be using it again back at the desk for a longer period?

Is there ever a good time to just use it with the power cord plugged in or should I always be using the battery?

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7 Answers

dpworkin's avatar

I use my home-based laptop which never moves with the power cord plugged in 24/7. I use my netbook battery only, and charge it only when discharged. I guess it depends upon the circumstances, but if you use battery at all, you are better off avoiding the power cord until the battery is ready to be charged.

majorrich's avatar

This is something I am struggling with even as we speak. I use my Macbook for lecture notes and my book, but my battery is all wonky. I have a battery monitoring program that tracks capacity and level of charge. I can turn on the laptop and one time it thinks it is at 60% capacity and 100% charge and later I can turn it on it thinks it is at 85% capacity and 90% charge. I called Apple and they told me to run the battery completely flat once a month and let it sit dead for at least 5 hours before I charge it back up. I am charging now. Will let you know how it works. I assume it works pretty much the same way for most laptops.

jrpowell's avatar

A lot of the battery bullshit is old info from the Nickel Metal Hydride battery days. All recent batteries are Lithium Ion and don’t have the same problems.

Just plug it in when you can and enjoy the full charge when you have to leave the house. Even if you beat the shit out of the battery it will work well for a year. Just toss 50 cents in a jar everyday and don’t worry about it. Use the jar money for a new battery when you need it.

Managing your battery usage is huge pain in the ass, worthless, and time you should be spending making love to your significant other.

b's avatar

While it is true that lithium batteries do not have the same issues that the old nickel metal hydride batteries did, but they still need some basic care. You just have to remember to occasionally use your battery. It is also good to fully discharge your battery every couple of months. That’s it, nothing complex.

jerv's avatar

While LiON (Lithium-ion) batteries need a full discharge from time to time to recalibrate, you only really need to do that once a month. That old “run it until it’s dead before charging” is a holdover from the days of NiCads (Nickel Cadmium) since NiCads had a horrific “memory effect”. LiON batteries do not have that, but they lose capacity with temperature and exposure to oxygen. If you can breath, a LiON battery will wear out regardless of how/when you charge or use it.

You should unplug it if it’s fully charged and not in use though. The little trickle of energy it uses to stay topped up creates just enough heat that, over the course of a couple of years, it will add up and take a few percentage points off of your capacity. I unplug my laptop at night and when I start it up the next day, it has ~98% charge left, and what is “missing” has to do with the fact that I usually put it to sleep instead of doing a full shutdown.

Contrary to what others have written, NiMH batteries do not have much of a memory effect (if any). That is part of why they replaced NiCads. The Toyota Rav4 EV has a large-format NiMH battery and most of those got at least a decade (around 150,000 miles) on their original battery.

Frenchfry's avatar

@majorrich Ill be cheking back too. I am wondering why that is too? I don’t know if I can go five hour without a computer though. HMMM

LuckyGuy's avatar

I just answered this in another Q. Here’s what I wrote:

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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