Should you run your laptop on battery or charger power?

Should you run your laptop on battery or charger power?

Summary: An interesting article in Slate by Jacob Leibenluft the other day asks a simple question:Do you save more energy keeping your laptop plugged in during use, or should you use your charger only after the battery runs out of juice?

TOPICS: Laptops, Hardware

Power PlugAn interesting article in Slate by Jacob Leibenluft the other day asks a simple question:

Do you save more energy keeping your laptop plugged in during use, or should you use your charger only after the battery runs out of juice?

It's a complicated question, with even more complicated answers, since different manufacturers give slightly different answers: Lenovo and Dell reportedly say your battery should be fine if your computer stays plugged in; HP says you should remove the battery if you are running on AC power for weeks at a time; Apple suggests you should unplug and run off the battery every once in a while.

So who's right?

Assuming you use the same energy plugged in and not, you're probably better off staying plugged in, because energy is lost in the process of charging the battery, storing the electricity, and then powering the computer from the battery, according to Leibenluft.

A report (.pdf) prepared by the Natural Resources Defense Council five years ago estimated that running a laptop from AC power is about 20 percent more energy-efficient than doing it off a battery.

But that was five years ago, ages in tech time. Leibenluft reports: "Even if battery charging systems have improved since then, common sense suggests that using AC power requires less energy."

The article takes the green angle, noting that just by using a laptop (and not a desktop), you're already saving money, since laptops are far more efficient and require less energy to manufacture than their boxy counterparts.

If you contend that keeping a laptop plugged in damages the life of the battery, it's an even tougher call: Batteries require an awful lot of energy to manufacture, and there's an environmental cost to recycling a spent one, so what's worse in the long run?

But that's the global view. What about the energy bill you pay for at the end of each month?

The final tally can also be affected by this caveat: most laptops are set up to use less energy when they aren't plugged in, since battery life is at a premium, so as soon as they start receiving AC power, they're more inclined to kick it up a notch, performance-wise (brighter screen and so forth). So if you've never touched your laptop's power settings before, chances are it uses more energy when it's plugged into the wall.

So who's right in this debate? It's still unclear, and the vampire suck of your computer's power adapter only makes matters worse.

Do you plug in or unplug when you use your laptop? Tell us in TalkBack.

[poll id=8]

Topics: Laptops, Hardware

Andrew Nusca

About Andrew Nusca

Andrew Nusca is a former writer-editor for ZDNet and contributor to CNET. During his tenure, he was the editor of SmartPlanet, ZDNet's sister site about innovation.

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  • It shouldn't be that hard to figure out.

    It really shouldn?t be that hard to figure out. Get a power meter and run three tests. First test run laptop at full settings while plugged in with no battery. Second test run laptop for same period turn off laptop and see how much power it takes to charge it. Third test run laptop plugged in at the same power savings settings as on the battery to see how much power that draws.

    Well not truly scientific it should yield a good result.

    My bet is that the laptop with limited settings while plugged in would be the best. As the conversion from ac to battery and then battery to pc is a excess waste.
  • Slow news day?

    The actual difference in energy consumption between mains and bettery power, even at 20%, is unlikely to yield any worthwhile savings. Better to save 1 litre of fuel per week by driving more carefully (or getting a more efficient car) or change incandescent bulbs to fluros.
    Fred Fredrickson
    • A note...

      [i]Better to save 1 litre of fuel per week by driving more carefully (or getting a more efficient car) or change incandescent bulbs to fluros.[/i]

      Actually, just checking your tire pressure once a week will save fuel; most cars today have at least one tire underinflated, and that wastes fuel. I agree about the driving habits, that makes a big difference, as well as what the car is used for (some cars give better fuel mileage than other for certain types of driving), and also using synthetic oils and changing or cleaning (reusable air filters for example) filters regularly. Getting a more efficient car CAN be an option, but keep in mind the cost of fabricating parts/ building/ shipping/ etc of the new car and the cost of disposing of the old one (is someone else going to use it?).

      Sometimes a proper tune up will do more (i.e. have less impact on the environment) than replacing the vehicle. If you have a large family and your 4 cylinder engine is always struggling, you may find that a larger engine will save fuel.

      On a recent 300 mile round trip, we found that a 30 year old full sized pickup truck used significantly less fuel than a brand new similarly sized (and loaded) supposedly fuel efficient truck. Of course the old truck didn't have all the bell and whistles the rental did, but both did the same trip on the same day in convoy, alternating as lead, and the new truck used almost 11% more fuel.

      It's not always as simple as checking what the sticker says...
  • Battery life

    The real problem with the batteries, is that they tend to deteriorate over time. And it has been suggested in the past that by keeping your laptop with the battery in it, and plugged to the power outlet at all times, actually causes damage to the battery and causes it to be more energy inefficient, not storing energy and actually wasting more energy.

    What I tend to do is that if I will run the laptop off a power outlet for a long period of time and the battery is fully charged, I simply put the machine to sleep, remove the battery and resume whatever I was doing. If I need to move out and still be working (for the amount of time that the battery gives power to my laptop) I simply put the battery back in and off I go. I usually keep the power saving settings for my laptop in such a way that both AC powered or baettery powered it uses pretty much the same amount of energy (i.e I use a powersaving profile rather than a peformance profile while on AC, unless I require the extra computing power)
  • depends...

    Which is best depends on the battery technology and the details of the laptop power supply. Nicad batteries have a sort of chemical "memory" that adapts the amp-hour capacity to the depth of cycle. If you constantly discharge to half of capacity and recharge, after awhile the battery thinks that what is rated as 50% is 0%, and will run out of gas at that point, not totally but with only limited current down to the true 0% point. The battery can be rehabilitated by allowing it to go all the way down before recharge. However, who wants to do that with a laptop that is prone to being grabbed and carried away on a moments notice? You want it ready to go all the time. Therefore, I keep mine on constant charge but when I am running on battery will run it till it beeps for relief, which often happens before I can get to an outlet. Note that it takes a number of cycles to build up the memory effect. There is little harm in partial discharge/ recharge so long as there is deep discharge once in awhile.

    NiMH and lithium chemistries do not have memory effect, but every type of secondary cell (rechargable) has a limited number of rated cycles beyond which performance begins to plummet.

    As for the internal power supply that is driven by either the battery or charger, some cheaper chargers will soar in voltage without a battery to help stabilize power demand. Better chargers do not. The internal power conditioning circuitry should be able to handle the higher voltage anyway, but I'm just saying that most designs assume that a battery is always present. I consider that to be a reasonable assumption. Constant charge at low levels is harmless, constant charge at high levels is problematic. Virtually all laptop supplies have intelligent charging circuits that monitor charge level and switch from fast to low level charge rates as soon as the battery is topped off. As for energy consumption, I agree that compared to the value provided by the computer and the small magnitude compared to other appliances, it's a trivial, ignorable issue.

    You might want to keep informal tabs on the time that your laptop will run from full charge to end of charge capacity. It drops over the life of the battery. If you reach half the original running time, a replacement battery might be in your future. Or, if enough years have passed in the interim, a new laptop.
    • Thanks!

      I just purchased a new Dell XPS M1530 which is the 1st laptop I've ever owned. So this was interesting to me. I been messing around with computers for over 20 years. I even had a 9 node BBS for quite a while which was a ball for me.I've been running my laptop charging all the time and just keeping it just plugged in. I've got a ton of Dell's and no matter what anyone says they have been great for me. I used to put my own together for years but to me it's not worth it anymore, time wise. I'm hooked on this laptop and glad I went that way this time. I'm going run my Battery down now. My last computer is aked out Dell 400 P4 w/ 3Ghz 4meg of RAM. Still runs stronge, I put a power supply in it and that's it. It's been online 24/7 for over 3.5 years. twim HD's with With SS. Can you tell I still love that box? LOL! Thanks for the info on Battieies. Think I'll run my batteries down and recharge the later. Any other info let us know~
    • Just common sense

      I just keep my laptop plugged into the wall with the battery installed. When I use it, the battery is in effect an uninterruptible power supply. That's just common sense to avoid lossing data or screwing up the OS.

      Since HP recommends removing the battery from their laptops, I have to wonder about them. Do they have any engineers working there?
      • Re: Just common sense

        One of the other reasons stated for removing the battery from a laptop if it's plugged into AC for extended periods of time, is to extend the long-term life of the battery. Even if the charging circuitry disconnects the battery when it is fully charged, the battery is still physically enclosed in the laptop case, which is a pretty warm environment when the laptop is running. The chemistry of Li-ion batteries degrades when the battery is in a warm or hot environment, whether it is being "used" or not. In fact, storing a battery, all charged up, in your fridge, will help slow down the natural and inevitable degradation of the battery chemistry. (Much like we used to store photographic film in the fridge.) So, yes, HP does have engineers (not me) who probably understand the battery chemistry very well, and that's why they made the remove-the-battery suggestion.

        Obviously, there's a trade-off with convenience, and possible damage to battery compartment hardware. If you're taking your laptop away from the AC plug on a daily basis, pulling the battery each time you fully recharge it is probably not worth the hassle. In our house, one of our laptops spends 99% of its time plugged in to AC.
        • I guess it comes down to personal philosophy

          I'm the guy who thinks 19 miles to the gallon is fine, so long as I feel safe in my car. Likewise, I think batteries are a cheap price to pay for data integrity. Lives and data can be hard to replace.
          • It's all relative

            [i]I'm the guy who thinks 19 miles to the gallon is fine, so long as I feel safe in my car.[/i]

            If you live, shop, work and play within a 10 mile radius I agree with you 100%. If you drive 1000 miles a week alone and with no cargo, then 19 mpg is pretty unacceptable. If you change your battery every 2 years, not that big a deal (as long as it's recycled properly). If you are replacing 1000 batteries every 6 months and they are going in a landfill then I have a problem with that.

            You may know that the largest commodity carried by US railroads is coal; care to guess the second? That's right, garbage.
    • Nice Response!!

      Well written and technically accurate. A true service to readers.

      I personally dislike Nicad batteries for the memory issue. NIMH seems like a good solution, but it also suffers from a cyle life issue, but not as severely as the issues of NIcad.

      Lithion-Ion batteries (As we've all recently heard about) are somewhat dangerous due to explosion and fire issues. I think it stems from inadequate system designs.

      Whatever battery used, the true secret to success is the charger! Laptop manufacturers typically don't spend a lot of money on their chargers. For a charger to work properly, it needs intelligence and sensing. I don't know of an aftermarket filling this niche, or if it's really important to most users!

      The best bet is most likely to run a laptop with the battery installed and plugged into the wall. Let the battery state fall when on the go, and plug it into the wall after the battery gets pretty low.

      The liquid fuel cell type power supply needs a fire lit under it!

      Retired Energy Engineer.
    • I want to know if this is the case with most

      new laptops. I would like to advise my students, most of which are very nontechnical minded. They do not want to use the batteries, but I think they should at least occassionally just for that reason, so their "memory" is not stuck at 50% or less. Secondly, should they take out the battery when using AC,i.e. Is it better for the battery not to be charging a full one? I think your answer is no;leave it in. Is that correct? Thanks for any advice.
  • Depends on the notebook

    Some newer notebooks have a feature that, once the battery is fully charged, automatically disconnects it from the power supply. Then, you are running the notebook as if you've taken the battery out. That's a sensible solution. You should check with your manufacturer.
    • Battery or Electricity

      As for my Fujitsu Lifebook, Model N6010, have to keep the power card plug'd in as the laptop is constantly using the battery power to keep it's workings active when turned off. Battery will last maybe a up to 4 hours of storage before going dead. Complained to Fujitsu since day 1 and was advised this is the way this laptop works and keep the battery charged.

      Not crazy about the power being plug'd in constantly, but so be it. Fortunately my in the field jobs have electrical outlets.
  • RE: Should you run your laptop on battery or charger power?

    Yeah. I use my laptop plugged in all the time. I have it set to turn off the monitor if I'm not using it for 5 minutes and then it goes into Standby/Sleep after 20. Simple enough.

    But I also like to keep the battery in it as well. Just in case while using it or not and it's on, if the power should ever go out, it's got it's own back-up.

    Batteries aren't that expensive anyway so even if it wears the battery down, I'm not worried.

    However to my knowledge most systems, even older ones, know that when the device is plugged in, it cuts off using power from the battery so obviously it doesn't use battery power at the same time. But LIKEWISE, the battery does not continually charge. When it's fully charged, the little light goes of on my laptop anyway, telling me it's done charging and that's it.

    Once in a while I unplug it to carry away but very rarely. So, when I do plug it back in, it charges the battery again for about 10 minutes probably.

    It's ironic as mobile as laptops are I never go anywhere with mine. I just like the simplicity of it. It's small, all in one place and only 1 chord.
    • RE: Should you run your laptop on battery or charger power?

      I am still not clear. As a layman what should I do. I have Dell laptop with 6 cell battery. I am a consultant who is on the move on daily basis but get power at most of clients. I generally keep AC on whenever I have to work more than 15 min. In last two years battery life seems to have degraded though. Pl. suggest.
  • You should do whichever consumes the most electricity

    I always run my laptops on AC power except when no such power is available. I even have a power inverter for my car, for when I need to use the computer away from home/office.

    Unless it's going to lengthen my battery life, there's no reason to worry about reducing electricity consumption so long as I can pay my electric bill.

    Columns like this just go to strengthen the truth behind my new motto: Green is the new Stupid.
    • Stupidity should hurt

      [i]Unless it's going to lengthen my battery life, there's no reason to worry about reducing electricity consumption so long as I can pay my electric bill.[/i]

      So you don't mind if we build a new reactor based power plant in your neighborhood to supply you with that extra power? Funny how people don't care up to the point when suddenly it's NIMBY.

      [i]Columns like this just go to strengthen the truth behind my new motto: Green is the new Stupid. [/i]

      That is truly the most ignorant statement I have ever seen on this website. Green is not stupid, people are stupid.
      LED bulbs will use 2 to 5% of the power of incandescent light bulbs, and will most likely last longer than you will own your house. Does it make sense to replace all your bulbs at once? Probably not. Does it make sense to set fire to your neighbor's SUV because it uses a lot of gas? Absolutely not.

      But if you have no regard for or concerns about ecology, give us your home address and we'll go bury all our old dead NiCad batteries in your back yard. We promise not to mess up the grass.
  • RE: Should you run your laptop on battery or charger power?

    Agree 100%.

    It's like "change" with no substance....
  • Another consideration is max number of recharges

    I thought I read somewhere that the typical laptop battery has a lifespan of 500 charges. So if you constantly charge and drain the battery, you eventually have to buy a replacement. And they ain't cheap.

    Might be why HP says remove it and run on AC only.