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Treat your tablet battery correctly

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There are a lot of misconceptions about batteries and charging. So many that I already wrote an article about it a year ago on Anything but iPod. One year later and here I am, talking about tablets instead of MP3 players. The same concepts are true for this new family of gadgets though, so I thought I’d resurrect my old guide and update it for the new year, the new site, and these new devices.

Charging: rumours and misconceptions

99% of all the rumors and misconceptions surrounding batteries for any electronic device have to do with charging them. A lot of “rules” on how to charge batteries are still around from the “old days” where electronics used completely different types of batteries, and has nothing to do with the reality today. Any modern gadget with a rechargeable battery will have a lithium based battery in it. Why this doesn’t say much, it’s very important when it comes to how the battery behaves. Most people have heard that you need to charge the battery for 12+ hours when you get it, leave it alone while charging, discharging and fully charging as often as possible etc. This is complete and utter nonsense when it comes to lithium based batteries. We’re talking a completely different battery technology, one which has a whole other set of “rules”. Here are some:

Lithium batteries don’t care when you charge them or for how long. All night, fine. 5 minutes at a time, fine. 10 times a day, go ahead.

There’s no priming needed, which means the first time you charge the battery is no different from the 100th time you charge the battery. You don’t have to charge it for an insane amount of hours, as the battery will shut down charging when it’s finished fully charging anyways.

Fully discharging the battery isn’t good for the battery. In most cases nothing bad will happen, but there’s a chance- especially if it’s stored for extended periods of time with no charge- that the battery won’t charge back up afterwards. The only reason to discharge it is in some cases where it will reset the battery’s ability to estimate the amount of charge left.

A lithium battery charges 70% of the capacity in 1/3 the total charge time, if charging from a fully discharged state. The last 2/3 of charging time is for topping off the battery. This has been very evident with my iPad when I’ve had to charge it a bit in the evening after using it all day (which is pretty rare, which says a lot about the battery life of that thing); it will pop up from 10% to around 50 in no time.

I'm normally a pretty frugal person, but I still compulsively buy any R/C aircraft that's less than $30. In the last few years, this has become a problem.

The total charging time however might depend on the charge you use. The iPad is a very good example of this, as it charges through a USB cable- meaning 5 volts. USB ports only give about 500-700mA though, which is basically the amount of power transferred at the specified voltage. If you connect an iPad to a computer, it says “not charging”, which isn’t strictly true as it simply charges very slowly. The iPad has a very large battery, and that is why the iPad charger is 2A, which is 2000mA. Multiply these, and 5v*2A = 10W. The iPhone charger in comparison is 1A, so 5W, which is half that of the iPad. Basically that means that charging an iPad through USB will take up to 4 times as long as doing it with the included charger, and twice as long with the iPhone charger. This also applies to other devices- for example the Archos 5 IT which I had last year, which was infamous for charging extremely slowly through USB but didn’t come with an AC adapter included (you could buy one separately)

This does not however mean that your iPhone will blow up if you connect it to the iPad charger, as it only draws as much as it’s built to when it comes to amperage.  A wall socket works the same way, with a constant voltage and a maximum amperage (anything from 15A and up) and a lot of different appliances using different amperage but the same voltage. Basically, if the voltage is the same and you can physically connect a charger to a device, it will work.

There are also other things to consider, but that are less important to the average user. If you want to geek out with battery information, take a look at the info over at Battery University. I especially recommend people take a look at the “do and don’t do” comparison chart for various battery types. They also have some info specific to lithium batteries that is interesting.

Maximizing battery life

Battery life, meaning how long the tablet will last on a charge, varies greatly between different devices. It can range from just a couple of hours on the crappiest of crappy tablets (and those that run Windows…..) to 10-12 hours on the iPad and some upcoming tablets and weeks of use on e-ink devices that only use power when the page is turned. The actual number of hours you get out of a device depends not only on the capacity of the battery, but also how effectively the device uses the power. That is the main cause of the difference in battery life between something like an Android tablet an a Windows tablet, as the latter can’t run properly on hardware as slow (relatively speaking) as the energy efficient components used in the former. You might be surprised to know that the iPad battery is only 25Wh (Wh = Voltage*battery capacity in Ah), which is slightly less than the 29Wh battery in the Dell Duo, a convertible 10″ Windows tablet. While I can attest to the iPad going strong for 12 hours and longer, testing has shown the Dell Duo to give up anywhere from 2.5-3.5 hours. My 13″ ultraportable laptop can match the iPad’s battery life, but requires a 84Wh to do so. It’s also important to look at what battery results people get in real life and in different usage scenarios, as manufacturer ratings are often optimistic (though for the ipad they are in fact pessimistic for some reason).

That brings us to what you can do to prolong the battery life of your tablet. The rule of thumb is that the more hardware is in use, the more the battery will drain. That goes for CPU/GPU activity as well as various modules (GPS, WiFi, 3G etc). A tablet with no Internet connection, no Bluetooth active, no GPS in use, screen brightness at the lowest and only running very simple apps would definitely get a few more hours on the battery than the tablet next to it that’s playing Need for Speed while streaming music from the Internet and running a GPS tracker in the background. Personally though, I don’t worry about it with the iPad, but with other devices I at least turn down the brightness if I know I’ll be using the device for many hours.

The other definition of battery life is regarding how many times you can recharge the battery before it gives up. First off, let’s get some more rumours and misconceptions out of the way. Laptop batteries often serve as a worst case scenario as they often lose their capacity a lot faster than anything else. This is due to several factors, but heat is often a major factor as anything that’s a full blown PC generates more heat than a low power portable Android tablet. Still, 500 recharge cycles (which is a number often thrown in for good measures with lithium batteries) is only about 1.5 years with daily charges, while others (like Apple) put the number closer to 1000. It’s not like the battery will go from working fully to being completely dead though, so you’ll gradually lose capacity over time. Tablets generally don’t have user-replaceable batteries (though some do), but even Apple doesn’t charge more than $100 for an iPad battery replacement and that isn’t half bad in my opinion if you can recharge it 1000 times (daily for 3 years) before it dies completely. By then, you’ll probably want a new one anyways as your device might not be updated any more and be left behind in other ways way before the battery gives up.

To make sure that you get as many charge cycles as possible though, there are some simple guidelines you can follow. Avoid extreme temperatures both hot and cold and just charge the player when you need to. As a rule I try to charge my iPad once a day, but I’m not beating myself up over doing it twice if it’s a day of very heavy use. With other tablets it might be more of a problem because of much shorter battery life, but a tablet is there to be used- so use it!

Bottom line

The point of this article is to get some pieces of misinformation set straight and put some things in perspective. With lithium batteries, the best thing you can do for your battery is to completely ignore how and when you charge the battery and just make sure you have enough power when you need it. Lithium batteries are made to serve the user, not the other way around, and the “tips and tricks” that are left from the old days of other types of batteries actually hurt lithium batteries.

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Andreas Ødegård

Andreas Ødegård is more interested in aftermarket (and user created) software and hardware than chasing the latest gadgets. His day job as a teacher keeps him interested in education tech and takes up most of his time.

Avatar of Andreas Ødegård

55 thoughts on “Treat your tablet battery correctly

  • Avatar of bolliby

    That’s a lot of info

    Reply
  • Thanks for that. Another nicely done article. Keep it up! :)

    Reply
  • Avatar of copeys

    “Avoid extreme heat”

    Did you know that the iPad/iPhone will turn not function if it’s too hot?? … How do I know? Mine turns off all the time! Haha. Wasn’t built for the heat out here!

    But a very interesting read. Particularly like how you said that when a device’s battery (such as a tablet) shits itself, that it’s just better to get a new one cause the devices have improved a lot by that time anyway!

    Reply
    • It’s the opposite over here…too cold. Most electronics can only handle about -20C (-4F), which isn’t exactly uncommon in Norway this time of year

      Reply
      • Avatar of copeys

        Not uncommon…. Thought it was always that cold over there ;) :P haha
        You reckon after all these years that they would be able to develop a product that is able to operate efficiently between -30 to 50C. Like.. How hard can it be?!? :p

        Reply
        • Actually quite hard. Batteries are severely affected by cold, and so are LCD displays- you can literally see them (the displays) get slower in the cold, with ghosting etc. The jump from -20C to +20C (inside) can also cause condensation and water damage

          Reply
  • This article would’ve come in handy a few years ago, would’ve saved me a lot of time trying to care for my now deceased laptop battery :)

    Reply
    • I pulled a dead battery out of an old laptop only a few days ago. 3.5 years old. Probably the most overheating laptop I’ve ever had (or seen) and it still lived that long. Of course, battery life at the end was close to nothing.

      Reply
      • Mine lasts about 5 minutes nowadays, but it is old, over 3 years, I think… I try to think of it as a smaller desktop computer :P

        Reply
        • Yeah mine is also on the “past 2 years old slope” where it is starting to drop off dramatically. Soon it will be good enough to get me from one power adapter to another. So yeah, a portable desktop is exactly what it is.

          Reply
  • Wow good to know. I will stop worrying about my laptop battery from now on.
    I would always take the battery out if it was charged and my laptop was plugged in.

    Reply
  • Avatar of allen schmidt

    Good to see the info on this. We hardly think of battery care, but think of battery endurance plenty.

    Reply
  • my 1-year-old netbook only charges back to 65% now. disappointed.. i tried my best to keep away from extreme temperatures, but it’s hard to do that at night when i’m in bed and downloading a lot of media. seem to be dying way too soon, but oh well…

    Reply
  • Avatar of Calvin

    Great article, I really appreciate the info.

    Reply
  • I never did understand the talks about priming a battery. I still tend to nearly drain my battery on my MacBook before a recharge for good measure, though I di agree I see no real difference in practice here.

    Reply
    • I think the whole priming thing is true with other types of rechargable batteries. Maybe NiCad or NiMH, but don’t quote me on that.

      Reply
  • Avatar of johnnyfive

    …and now when we’ll get the the anti-matter batteries? But please Sony stay out of it!!

    Reply
  • Avatar of seroson

    I feel this needs to be known for all types of batteries.

    There just isn’t enough basic mainstream info about this kind of stuff

    Reply
  • Avatar of Matthew B.

    Most of my friends are still priming batteries, trying to drain them completely before use.. I tried convincing them that doing that is wrong and will only destroy the battery, but I guess one can’t break the old habits..

    Reply
  • Avatar of JosephM

    I think everyone should read this article. Especially my sister.

    Reply
  • Is this true for modern laptops as well?? I still read that they need to be disconnected from the powercord regularly, and allowed to discharge, although I usually don’t like to be bothered w/ that.

    Reply
  • Is it OK to run the tablet like a laptop — i.e., with the charger plugged in? Or will it get upset when the battery’s fully charged and I haven’t unplugged it yet?

    Great to know I can start using the thing now instead of waiting 12 hours for the battery to charge; thanks for the info!

    Reply
  • i just got a tablet and it says to charge it for 6 hrs. Will it hurt it if i don’t???
    PLEASE HELP!!!!

    Reply
    • Charge it until it’s fully charged. Feel free to use it while you do. It physically stops charging once it’s full so do what you want with it then

      Reply
  • Avatar of Anthony

    Im still a bit unclear, is it bad to leave your lithium battery plugged in even when it is fully charged? Ie. Plugging my phone in overnite while I sleep even tho it is at 80% battery life

    Reply
    • Yes and no. Bottom line, I do it. Especially now that I have a phone with a replaceable battery, though I’d do it anyways

      Reply
  • Helpful, thanks! When you say “500 recharge cycles” what does that mean if I’m usually, say, only 25% discharged when I recharge? Does such recharge count as a full cycle (roughly 1/500th of my “allotment”) or as 1/2000th of my “500 recharge cycles” “allotment”?

    Also — a separate issue — did I draw the right conclusion: Since I use my HP Touchpad around home where I can plug it in frequently — or on occasional one-day plane trips where I can get it up to 100% before I fly — I don’t need to replace my lost 10W HP charger and can just rely on a standard generic USB charger (even though the Touchpad warns me about using “a source that provides less than the recommended voltage or current” each time I plug it in).

    Reply
  • Very clear and helpful advice. Thank you.

    Reply
  • What happens if I have the tablet is always kept in charging mode? Will the battery drain down within months or will it not matter at all.

    Reply
    • If the tablet is always charging the battery will wear down eventually, because it’s operating at a voltage it shouldn’t

      Reply
  • Avatar of ananthudk

    this was indeed an eye opener…but i have a doubt…..i didnt charge my tab for the first time i opened it….tried some of the features and then plugged it to charge.(the initial charge was some 24%)
    i charged it for the whole night and next day, when i started using it, battery is draining off fast.i.e. it lasts only one hour long….any suggestions???
    btw ur article was well written…:)

    Reply
  • Avatar of Asim Iftikhar

    Is it okay to charge my Android phone and tablet on a UPS?

    Reply
  • Avatar of Dennis D. Mennis

    great info..i’m using my first tablet,know nothing about them(i’m a tablet virgin) and was battery paranoid about charging and recharging,etc..something is draining my battery and I’ve already uninstalled the weather app because of that.but it still only stays charged for an hour at the most.no running apps.i surf sites but don’t do a lot of downloading.don’t know why i’m having to charge after an hour’s use..people tell me they play videos and stuff and theirs lasts for several hours.wish I knew why mine won’t

    Reply
  • Avatar of Frances

    Thanks so much,, thought I was doing the wrong thing unplugging my ipad even when it’s not fully charged! Thanks Again!

    Reply
  • Avatar of Abdullah

    i am charging my novo tablt with iphone charger.. .. ..is it harmful for my tab because today it make my tablet hot without increase in charging, i chage it for an hour.. .. ..what should i do?

    Reply
  • Avatar of Abdullah

    answer me it’s realy serious..

    Reply
    • Avatar of Andreas Ødegård

      I cant answer questions about devices I dont have, but if it gets dangerously hot, it’s fairly self explanatory that you stop charging it that way

      Reply
  • Avatar of Abdullah

    it’s simple tablet 7 inch.. .. .. ..is iphone charger good option to xharge my tab?

    Reply
  • Avatar of Martyn Orton

    Hi, brilliant!!!!!
    Can you tell me if it is OK to leave my charger in all of the time? My thinking is if it is in all of the time, then the battery won’t be used. Just like a portable CD player! My tablet is a cheap 9″ CNN android tablet,
    Many thanks

    Reply
    • Avatar of Andreas Ødegård

      Dont do that. It will keep the battery at 100%, which keeps it above the ideal voltage, and will actually nake the battery go bad quicker

      Reply
  • Avatar of Martyn Orton

    Sorry, I mean a CNN tablet.

    Reply
  • My mid tab get hot over a short period of usuage,I hv to wait till it cool before I can use it. And by den d battery will be drained to zero percentage.ani help

    Reply
  • Avatar of kushantha

    wow nice , you gave me great idea about tab batteries.

    Reply
  • Avatar of haycope

    just bought a brand new Google android PC tablet. The battery only last approx. 30 min. Bad battery or is that just the nature of the beast?

    Reply
  • Avatar of daryl

    heyy i have a hipstreet aurora tablet if i use it while it is chargeing is tht bad for the battery or does it matter

    Reply
  • Avatar of bruce

    I havent charged my tablet for a year. Is this bad or will it still work? I need answers please..

    Reply
  • Avatar of usman noor

    Hey author,
    I have samsung galaxy tab 2 10.1 , its battery is drained 3\4 times and now this time it is not turning on so, please help me regain that I’ll be very thank full to u.

    Reply
  • Avatar of Taylor Corbin

    I left my house for a week and accidentally left my tablet charging the whole time. On the screen it says it has no battery power left and wont turn on at all except to say that what can i do to fix it.

    Reply
    • might help if you mentioned what tablet you have.
      Unplug it and leave it for a day, plug back in.

      Reply
  • Please stop talking about planned obsolescence as if its a good thing!

    Reply
  • It will fail, almost all tablets take 5v, but the car battery is 12.1 to 10.8 volts! Your husband is lucky the tablet did not explode!

    Reply
  • Avatar of btillman

    If nexus 7 left on space heater for a half hour can battery be estroyed

    Reply
  • Avatar of Namakabrood Abrood

    Then How come iPhone users are constantly running out of juice at coffee shops and airports? My Moto can last 48 hours.

    Reply

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