Rechargeable Battery Problems: Overcharging, Leaving It Plugged In

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This thingie will run a lot longer on a full charge, and have a longer life expectancy overall, if you don’t overcharge it.

Does it seem like your thingie isn’t holding its charge as long as it used to, or like a full charge doesn’t give you as many hours of use as it used to? Does it seem like your last thingie died a lot sooner than you expected? It’s recently come to my attention that many folks don’t know two crucial things about charging their devices with rechargeable batteries, and that’s where the trouble begins.

DON’T OVERCHARGE

Rechargeable batteries lose a little bit of their holding capacity every time they’re overcharged. By “overcharged”, I mean when they’re plugged into an outlet for charging beyond the time it takes to fully recharge the battery.

**UPDATE 1/23/14** To anyone who’s thinking it’s not possible to damage a rechargeable Lithium Ion battery by leaving it plugged in too long, see this DMM post, where I discuss the difference between what’s technically correct about Li-ion batteries vs. real-life usage and performance, using the Boeing Dreamliner battery fires of 2013-14 as an example of real-life Li-ion battery failures due to overheating.

Plenty of people are in the habit of plugging in their device at night before bed and leaving it plugged in all night. DON’T DO IT! Even a fully-drained rechargeable battery should take six hours or less (usually, MUCH less) to reach a full charge, so leaving your thingie plugged in all night pretty much guarantees you’re overcharging* the battery.

*4/27/13 UPDATE: based on a comment made by a reader, I’ll clarify that where I say “overcharge”, I’m referring to damage caused both by what electrical engineers technically consider “overcharging” AND the overheating that can occur when certain types of rechargeable batteries are left charging longer than is necessary. Both types of damage are caused by leaving a rechargeable battery plugged in to charge for too long, so for simplicity’s sake I’m referring to both as “overcharging”. If you want the technical nitty-gritty, scroll down to my lengthy reply in the comments section below this post.

This practice reduces the capacity of your rechargeable battery bit by bit, meaning that a full charge lasts a little shorter each time you recharge, and since rechargeable batteries can only be recharged so many times, it’s also reducing the life of your battery overall.

For devices where the battery can’t easily be replaced, this practice means you’ll have to buy a new device that much sooner, too.

Some manufacturers have started making charger stations with a built-in timer that stops charging after a set period of time, usually about 4.5 hours. That may solve your overcharging problem, but it doesn’t address the problem of paying for the electricity the charger continues to draw from the outlet even when it’s not charging anything. Read on:

Sure, it’ll look great on your desk. But it’ll also be adding to your electricity bill every minute of every day.

 

DON’T LEAVE THE CHARGER PLUGGED IN WHEN YOU’RE NOT USING IT

The vast majority of chargers draw power anytime they’re plugged into the wall, whether they’re actually charging a device or not. You can get specially designed chargers that don’t do this, but they’re expensive and the charging cables that come with devices aren’t of this special type.

While it’s true that regular charging cables draw less power when they’re not actively charging, the bottom line is that you’re still paying for electricity that’s going nowhere.

So while those little electronic device caddies with holders for each of your devices, little openings for each cable, and a plug that’s supposed to stay in the outlet at all times may do a bang-up job of de-cluttering your desk or kitchen counter, using them pretty much ensures you’re paying for watts you’re not using.

 

 

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26 Comments

  1. Comment by Rebecca:

    I’ve always wondered what the secret is about these things. And dang, I just left my Kindle plugged in all night last night. :-( I’ll be better. Thanks!

  2. Comment by Linda Holz:

    left one of my kindles in over night and killed it. had to get a new one. :(

  3. Comment by P:

    Thanks for the hint! Did not know this before and now I will definitely unplug before going to sleep.

  4. Comment by gloria:

    Thank you so much!

  5. Comment by sandee mcminn:

    PLEASE remove the widget. I want to read the whole article about recharging the battery and can’t see some of it.

    • Comment by Mom:

      I don’t know what widget you’re talking about, since there’s more than one on this site, but just use the green Print Friendly button to view a given post’s content in a totally separate, text-only view. The button appears at the bottom of every post when you’re viewing the post as an individual page—as opposed to viewing it by scrolling down on the front page of the site. If you don’t see it for a given post, just click on the post’s title to view the post as a separate page. Then scroll down and click the Print Friendly button.

      I can’t control what computer, browser version, or browser settings every site visitor chooses to use, and some older browser versions or zoom settings can cause display problems, so I’ve provided this Print Friendly button for those who need it. But just so you know, the site is designed to work and display perfectly in Internet Explorer 9 and Firefox 20.0.1 with zoom set to 100%.

  6. Comment by Karen:

    Apple support told me that the more I kept my device plugged in the longer the battery would last because it isn’t using the battery while it is plugged in.

    • Comment by Mom:

      This statement: “the more I kept my device plugged in the longer the battery would last because it isn’t using the battery while it is plugged in,” is only applicable to times when you’re using the device, such as having a laptop plugged into a wall socket while you use it. This post is about charging your device when you’re NOT using it, and specifically addresses the common habit of leaving devices plugged in overnight to recharge.

    • Comment by Mom:

      Also, in terms of recharging only, it’s true that I’ve simplified things for purposes of this post and the technical details of different types of rechargeable batteries are a little more complex.

      Many recent-model portable electronic devices with rechargeable batteries use Lithium Ion battery cells, and while it’s right that these batteries will not technically “overcharge”, it’s still not safe to leave them plugged in longer than is necessary to reach a full charge due to the danger of overheating. While Li-Ion cells cannot be overcharged due to built-in override mechanisms in the battery which automatically cut off the charging circuit at capacity, so long as the charger is plugged into the battery/device it is generating heat. This is why every now and then you hear of a device that literally explodes: the battery has caustic and flammable chemicals in it, so overheating is very bad.

      Most rechargeable portable electronics that *don’t* use Li-Ion batteries use Nickel Cadmium batteries, and these most definitely CAN be overcharged and damaged by overcharging. Per the GP Nickel Cadmium Handbook, “Sealed Ni–Cd cells consist of a pressure vessel that is supposed to contain any generation of oxygen and hydrogen gases until they can recombine back to water. Such generation typically occurs during rapid charge and discharge and exceedingly at overcharge condition. If the pressure exceeds the limit of the safety valve, water in the form of gas is lost. Since the vessel is designed to contain an exact amount of electrolyte this loss will rapidly affect the capacity of the cell and its ability to receive and deliver current. To detect all conditions of overcharge demands great sophistication from the charging circuit and a cheap charger will eventually damage even the best quality cells.”

      Therefore, based on what Apple support told you, your device probably has a Li-Ion battery. However, they STILL should’ve advised you against leaving it plugged in longer than necessary when recharging it due to the danger of overheating the battery, which will reduce the battery life just as surely as overcharging a Ni-Cad battery. Overheating, overcharging: they’re kind of the same thing, outside of electrical engineer circles.

      And for those of you wondering why I didn’t spell out all these technical details in the original post: this blog is all about explaining high tech in plain English, and keeping things as simple as possible. This reply has gotten pretty technical, and the bottom line of the original post is still the same: it’s a bad idea to leave your thingie plugged in to charge any longer than necessary, no matter which specific battery type it uses and which specific thing could go wrong with that battery.

  7. Comment by Donna:

    How do you replace the battery of a kindle fire? Mine has been like this since I got it, has never held a charge like they claim.

    • Comment by Mom:

      Kindle Fire batteries aren’t meant to be replaced. Please see this article Why Does My Thingie’s Battery Die So Fast, for tips on extending battery life. Just switching to airplane mode when you don’t need wifi will GREATLY extend your battery life. But if you believe the battery is truly defective, contact Amazon to see if they will replace it for you. This is easiest if the Fire’s under warranty, but even if it’s not, Amazon may be willing to work with you if you explain that the battery has been a problem for as long as you’ve owned your Fire.

  8. Comment by Irene Shooter:

    This article has been so so helpful to me.
    Thanks a lot!
    ireneshooter@sbcglobal.net

  9. Comment by Jason:

    Unlike the nickel-based batteries of old, the lithium-ion batteries found in smartphones and tablets do not suffer from overcharging. This means you’re free to charge the battery at any point during each cycle without affecting the amount of charge it holds. Likewise, you can continue to leave it plugged in after it has reached 100 percent.

    Once the battery reaches about 90% of full, the charging system reduces the charge rate to a “trickle” and will continue to gently “top off” the battery to 100% – once it reaches 100%, the phone’s charging system actually shuts down charging altogether. So overcharging the battery is not an issue

    • Comment by Mom:

      With respect, you’re incorrect. Per BatteryUniversity.com:

      “Li-ion does not need to be fully charged, as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge, because high voltages stress the battery.”

      “Li-ion cannot absorb overcharge, and when fully charged the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium, and this could compromise safety. ”

      “Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage.”

      Also, it isn’t the battery that controls the flow of power during recharge, it’s the charger. As I mention in the article above, while higher-end chargers will automatically shut off when the battery reaches capacity, most chargers that come bundled with consumer electronics are not of the high-end type and do not automatically shut off.

  10. Comment by kgamiel@islandedge.com:

    Wow, this article is totally wrong for most modern devices, including the ones on the table in your picture. Li-ion batteries require circuitry that stops the charging automatically when the battery is fully charged. Therefore no electricity is being used, no heat is being generated, no damage is being done. There is no need to unplug the devices from the charger…ever.

    • Comment by Mom:

      kgamiel – This article is NOT totally wrong, and most Li-Ion batteries used in consumer-grade electronics are still at risk when they’re left plugged in beyond what’s necessary to get a full charge due to the likelihood of overheating (which is most definitely STILL a risk – read on for my sourced quotes from Battery University). You can read my lengthy comment above if you like, where I explain that for simplicity’s sake I am using the term “overcharging” to cover both literal overcharging and overheating conditions, because ultimately the results are the same: battery damage. This site is intended for non-tech-savvy consumers, not engineers, so I strive to keep things simple. As I’ve previously explained in the comments above:

      “Many recent-model portable electronic devices with rechargeable batteries use Lithium Ion battery cells, and while it’s right that these batteries will not technically “overcharge”, it’s still not safe to leave them plugged in longer than is necessary to reach a full charge due to the danger of overheating. While Li-Ion cells cannot be overcharged due to built-in override mechanisms in the battery which automatically cut off the charging circuit at capacity, so long as the charger is plugged into the battery/device it is generating heat. This is why every now and then you hear of a device that literally explodes: the battery has caustic and flammable chemicals in it, so overheating is very bad. ”

      Per BatteryUniversity.com:

      “Li-ion does not need to be fully charged, as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge, because high voltages stress the battery.”

      “Li-ion cannot absorb overcharge, and when fully charged the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium, and this could compromise safety. ”

      “Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage.”

      Also, it isn’t the battery that controls the flow of power during recharge, it’s the charger. As I mention in the article above, while higher-end chargers will automatically shut off when the battery reaches capacity, most chargers that come bundled with consumer electronics are not of the high-end type and do not automatically shut off.

      Finally, from Geek.com:
      “Any Li-ion battery has the potential to go up in flames, and that’s a product of its chemistry. Lithium is used in batteries as an anode because it has extremely high electrochemical potential. That is, lithium-ion moving to the electrode produces a lot of energy. Lithium’s low atomic weight is also useful in reducing the mass of batteries.”

      “While lithium is great for making high-capacity batteries, these same properties make it highly reactive and more prone to thermal runaway. Lithium is an Alkali Metal along with sodium, potassium, and the rest of the first group of the periodic table. Not only are these elements highly flammable, but they are so reactive that tossing a few grams into water will cause an explosion. So when a Li-ion battery does heat up, the lithium in it can accelerate the breakdown of other cells.”

      Yes, a perfectly manufactured Li-ion battery, when installed perfectly in a perfectly designed and flawlessly manufactured device, which is kept in ideal conditions and always operated within ideal parameters, is not at any risk of overcharging or overheating. But since in real life, imperfections abound in design, manufacture and use of consumer electronics, the likelihood of overheating still exists for the vast majority of batteries that are out there ‘in the wild’.

      • Comment by kgamiel@islandedge.com:

        I’m sorry, but it seems you’re still referring to older battery chemistry like NiCad and associated chargers. I sympathize, it’s a complex subject, but I find that misleading people who don’t know better is worth my commenting.

        The BatteryUniversity.com comments confirm my original post, I’m not sure why you’re referring to that. You are wrong that a charger must be “high end” in order to stop charging Li-ion. Li-ion *requires* circuitry to avoid overcharging, it’s a function of it’s chemistry. Most li-ion batteries have protection circuitry *inside* the batteries, including temperature protection.

        • Comment by Mom:

          I guess you didn’t read this part of my comment above:

          Finally, from Geek.com:
          “Any Li-ion battery has the potential to go up in flames, and that’s a product of its chemistry. Lithium is used in batteries as an anode because it has extremely high electrochemical potential. That is, lithium-ion moving to the electrode produces a lot of energy. Lithium’s low atomic weight is also useful in reducing the mass of batteries.”

          “While lithium is great for making high-capacity batteries, these same properties make it highly reactive and more prone to thermal runaway. Lithium is an Alkali Metal along with sodium, potassium, and the rest of the first group of the periodic table. Not only are these elements highly flammable, but they are so reactive that tossing a few grams into water will cause an explosion. So when a Li-ion battery does heat up, the lithium in it can accelerate the breakdown of other cells.”

          Yes, a perfectly manufactured Li-ion battery, when installed perfectly in a perfectly designed and flawlessly manufactured device, which is kept in ideal conditions and always operated within ideal parameters, is not at any risk of overcharging or overheating. But since in real life, imperfections abound in design, manufacture and use of consumer electronics, the likelihood of overheating still exists for the vast majority of batteries that are out there ‘in the wild’.

        • Comment by Mom:

          If what you are saying were true, that there’s no risk of overheating in Li-ion batteries, we would never hear of Li-ion batteries getting so hot that they’ve burned the consumers who used the devices the batteries are installed in, or news stories about electronic devices literally exploding due to an overheated Li-ion battery.

          EDITED TO ADD: Here’s yet another source in support of the notion that Li-ion batteries can easily become damaged, from howstuffworks.com:

          “Making lithium-ion batteries that can hold more power for a longer period requires vital components, including the separators, to be small and thin. The reduction in size makes it more likely that the batteries can fail, break, leak or short circuit.”

          • Comment by kgamiel@islandedge.com:

            Every consumer device in history that uses electricity has failed and caused damage at some point or another. As experience and safety regulations evolved, device safety has improved. I suspect toasters or irons have caused dramatically more fires and destruction than li-ion batteries. When circuits on li-ion batteries fail, it certainly makes for a sexier story, I admit, which tends to freak people out disproportionately.

        • Comment by kgamiel@islandedge.com:

          Looks like you edited your comment, I don’t know how to edit mine, so I’ll reply again. It goes without saying that circuits can fail and designs can be faulty. What does that have to do with leaving it plugged in overnight? Are you advocating only plugging something in to charge when you can be in the room to watch it? Do you leave *anything* plugged in, for example your TV or refrigerator? They all have circuits that can fail and cause fires, destroy your home, etc. If you’ve reduced your argument to “if protection circuitry is bad, a battery can fail and even start a fire”, then I think it’s time to humbly remove the article. Just my opinion.

          • Comment by Mom:

            Yes, I did edit it. And no, my bottom line is NOT “if protection circuitry is bad, a battery can fail and even start a fire” or that a device can be left plugged in overnight if someone’s watching it.

            My point is, and always has been, that there are LOTS of things that can happen to damage a rechargeable battery of any kind, and the most common of these things in the typical consumer’s world are overheating (Li-ion or Nickel cadmium) or overcharging (Nickel cadmium). On the other hand, if avoiding these possibilities is as simple as NOT leaving a rechargeable device plugged in overnight, then the sensible thing to do is NOT leave rechargeable devices plugged in overnight.

            You can certainly split all the hairs you want with me, but the risk of overheating is there and if avoiding that risk is as simple as unplugging devices overnight, I don’t see how that’s bad advice.

          • Comment by kgamiel@islandedge.com:

            I’ll conclude by saying that I think your blog is great and I applaud what you’re doing.

  11. Comment by CocoKoko:

    can it cause fire? because i left my ipad charging at home. and there’s no one left at home. i charged it yesterday (Saturday afternoon) and we’ll be back on Monday morning. please reply. thanks! :(

    • Comment by Mom:

      While it’s theoretically possible, it’s not very likely. I’ve Googled on every possible combination of the words “iPad”, “battery” and “fire” I could think of, and I couldn’t find a single report of an iPad battery catching or causing a fire. However, I think it IS pretty likely your battery’s holding capacity and/or lifespan will be reduced by leaving it plugged in for so long.

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