Could iPad heat have any damaging effect on the lithium polymer battery?

Discussion in 'iPad' started by TrimmTrabb, Apr 10, 2012.

  1. TrimmTrabb macrumors member

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    Apr 10, 2012
    #1
    I'm not trying to create a controversy, so no cynical replies please. I'm just looking for some informed opinion on this. Please don't reply if you're just wildly speculating.

    From Apple's batteries page:
    "If you use your iPod, iPhone, iPad, or notebook in temperatures higher than 95° F (or 35° C), you may permanently damage your battery’s capacity. That is, your battery won’t power your device as long on any given charge. You may damage it even more if you charge the device in these temperatures. Even storing a battery in a hot environment can damage it irreversibly."
    http://www.apple.com/batteries/

    There have been posts here suggesting wrapping the iPad in a towel and letting it run for 24 hours at max brightness to cure yellow tint problems and things like that. I haven't done this specifically, but for example, I used mine at 100% brightness for a couple hours while the iPad was lying on a bed, only to then notice that back got quite hot because the bed was acting as an insulator. When held in my hands, the iPad did not get as warm. No, I don't usually use it at anywhere near 100%, and I had just done it on impulse to test out the new display. People might also experience the same effect using a soft case that covers the back.

    Back to my question, I can't find anywhere on the net that tells you specifically what temperature a lithium polymer battery can safely reach before any irreversible damage, however small, might start to occur. The temperatures Apple gives are only ambient temperatures to operate the iPad in, but as I said above, even if your room is within that temperature range, wrapping iPad in a towel, or using it placed on a couch or pillow, or in a case, can create an environment for the iPad that is actually hotter than that.

    I'm not worried about burning my hands, but I just want a better idea for if / when I should be worried that my iPad's battery is not enjoying itself in there. I would like to think that the battery would have a high tolerance, but this doesn't seem to be the case when Apple lists a max storage temperature of 113...

    Any info from engineers or links to somewhere on the web to educate me on this would be great.
     
  2. seadragon Contributor

    seadragon

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    #2
    Good question. Heat is an enemy to electronics.
     
  3. kmanmx macrumors 6502

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    #3
    I doubt it.

    Batteries in RC helicopters, cars, trucks get far far hotter than those in electronics with little issue.
     
  4. TrimmTrabb thread starter macrumors member

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    Apr 10, 2012
    #4
    This is true, but are lithium batteries for those purposes shielded more heavily to protect against heat? To me, they look a bit thicker and more industrial than the iPad's batteries, which are very thin and seem (to my untrained eye) to be less shielded from the environment. Feel free to correct me on this.
     
  5. Jonesy76 macrumors newbie

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    Norwich
    #5
    +1
    You can hardly touch my racing cells for my RC cars when they're charging, or after a race when they've been discharged, and don't get me started on the heat from the motor also adding up the effect.
    My ESC's (Electronic Speed Controller) and radio gear are perfectly happy after receiving the heat they get.

    Anyway........have you felt the eat on the bottom of a MBP after a bit of use?
    Far more than the mild warmth you get on the back of the iPad.
     
  6. kmanmx macrumors 6502

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    UK
    #6
    Batteries for RC vehicles are tougher, but im not sure this is to protect from heat. They go through a lot more physical torture, being taken in and out, bashed around in rc vehicles etc - so that may be the reason for the tougher build.
     
  7. TrimmTrabb thread starter macrumors member

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    Apr 10, 2012
    #7
    Thanks for this.

    Are the batteries you use for your cars also lithium polymer? I understand different types of batteries have different heat tolerances.

    It's a good point about the MacBook Pro. I also have one. One thing I'll say in that situation is that the battery is kept well away from the logic board half of the case, which gets the hottest. In the iPad, the heat from the backlights at 100% brightness would be passing directly over the batteries to reach the back case. And we can also assume that the internal temperature of the case is hotter than the outside. I'm not saying this refutes anything you say, just a difference I thought may be significant.
     
  8. whtrbt7, Apr 10, 2012
    Last edited: Apr 10, 2012

    whtrbt7 macrumors 6502a

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    #8
    The heat actually helps the Li-ion batteries in the iPad. You actually get less power/battery life if the battery is colder (ie sub-zero temperatures). The lowest operating temperature of the iPad should be about 0 degrees celsius. The battery probably wouldn't work any lower than that. Excessive heat would damage the battery but you would probably have to use the iPad while you're sitting in a campfire. Lower temperatures would reduce performance and create power issues.
     
  9. sphinx99 macrumors member

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    Mar 31, 2012
    #9
    I design similar systems for a living.

    Generally speaking you start to see diminished life under discharge and (especially) charge conditions as you creep past 45C. At that point, it is in the interest of the device to start reducing its own internal charge and discharge limits to maintain battery life. Many consumer electronics devices do not, but this sort of behavior is commonplace in electric vehicle battery packs for example.

    My advice would be to let the device cool before charging it, if the temperature is 45C or higher. You could use it at high temperatures but try to avoid the heavy gaming at full brightness.

    whtrbt is incorrect that only excessive heat causes problems. At lower temperatures, internal resistance starts to spike and for a given current draw, you will see more open circuit voltage potential across the cell. This introduces its own set of reliability issues. You should not use the device at 0-5C temperatures.
     
  10. TrimmTrabb thread starter macrumors member

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    #10
    This is great. Thanks for that information.

    Would this mean that in instances where people have measured their (discharging) iPads at greater than 45C (and presumably the internal temperature is higher), you could start seeing battery damage? I'm thinking of the Consumer Reports test that reached 46.6C at room temperature, and a subsequent test at a 32C ambient temperature where the iPad reached 50C! By the way, in both instances, the iPad kept functioning and did not display a temperature warning or shut itself off. It would be unfortunate if the iPad was programmed to sustain higher temperatures and put itself at risk in order to remain on for users.

    Secondly, does damage to the cell occur as soon as a high temperature is hit, or does it require being at high temperature for a sustained period of time? If my iPad had reached 45C for an hour or two, would that likely have caused any damage? Thanks.
     
  11. whtrbt7 macrumors 6502a

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    #11
    If you're reaching temperatures in excess of 45 degrees while charging, you'll take a 50-60% hit to the battery when discharging at the same temperature. Basically what this means is to use the iPad from 0 to 35 degrees most of the time but if you charge and discharge at higher temperatures, you would take a hit to battery life. This is also "ambient" temperature and not "core" temperature. So if you're only heating up the battery in one specific place beyond 45 degrees celsius, you'll receive a fractional hit to battery life on the charge or discharge. Li-ion tech is pretty complicated and Apple states optimum operating temperatures for the battery. If you want awesome battery life all the time, you want to run your "ambient" temperature at 20 degrees celsius all the time. While the internal temperature of the spot near the A5X can reach about 36 degrees, it's not going to affect your battery life enough to really matter. If you are running the iPad and you feel the temperature is higher than your body temp by quite a bit, you may take a hit to the battery life by probably 20% depending on the situation.
     
  12. TrimmTrabb thread starter macrumors member

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    Apr 10, 2012
    #12
    Thanks. Just to clarify, though, there are 2 types of battery issues related to heat:

    1. Temporary reduction in the life of the battery before it runs flat
    2. Permanent reduction in the ability of the battery to hold a charge

    I believe you're speaking about #1 - the fact that a battery charge will last longer around room temperature, and shorter in higher or lower temperatures. However, I'm more concerned with #2 - the irreversible damage that can occur in the battery as a result of being exposed to excessive heat, and trying to figure out what "excessive" actually is.
     
  13. whtrbt7 macrumors 6502a

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    #13
    Ah I see what you mean. Li-ion batteries aren't designed to last forever. No matter what temperature you run the battery at, you'll get diminishing returns over time. So any device using Li-ion will have the following effects.

    Storage temp | 40% charge | 100% charge
    0 C | 2% loss after 1 year | 6% loss after 1 year
    25 C | 4% loss after 1 year | 20% loss after 1 year
    40 C | 15% loss after 1 year | 35% loss after 1 year
    60 C | 25% loss after 1 year | 40% loss after 1 year

    Permanent damage in my vocabulary for Li-ion would be an explosion/flame thrower effect/bomb. This normally happens in temperatures in excess of 150 degrees celsius. If you're li-ion battery is producing a LOT of heat like over 100 degrees celsius, you may be in for an unpleasant surprise. This could be caused by a short circuit on the battery or a battery chemistry problem and if that is the case, you should probably drop, stop, and roll :p.
     
  14. steve-p macrumors 68000

    steve-p

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    Newbury, UK
    #14
    I doubt it's anything to worry about. I'm sure we've all had the occasional time with iPhones getting very hot and that doesn't seem to cause battery damage. The iPad has a much bigger heatsink because of the large area of metal on the back too. Maybe covering the back with a case could negate that, and a small number out of the millions of iPads shipped may actually be defective, but otherwise I don't think it will affect the battery health much, if at all.
     
  15. spiderman0616 macrumors 68030

    spiderman0616

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    #15
    I would say don't worry about it. If/when the battery goes bad, just take it to Apple.
     
  16. sphinx99 macrumors member

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    Mar 31, 2012
    #16
    It's not an on-off effect. At higher temperatures, cycle life will start to reduce. However, a few minutes of charging at higher temperatures is not going to result in a noticeable impact.

    To put things in perspective, two or three full charge cycles at 50C is a good way to take maybe ~ 10% off your battery.
     
  17. TrimmTrabb thread starter macrumors member

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    #17
    Thanks. That helps to put things in perspective.
     
  18. avalys, Apr 11, 2012
    Last edited: Apr 12, 2012

    avalys macrumors 6502

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    #18
    I have learned not to obsess about taking care of material possessions as carefully as this.

    It is just a piece of consumer electronics. It is not a priceless treasure that must be preserved for the ages. It is not an investment that will appreciate in value if you take good care of it. Nor will taking obsessively good care of it have any substantial effect on it's resale value down the road. Use it for whatever you want, however you want, and don't worry about damaging it. It will be okay, trust me.

    In 2-3 years, it will have some dings and scratches, maybe 80% of the original battery life, and you'll sell it or recycle it and buy an iPad 5. This is inevitable. No matter how careful you are with it, that is it's fate. It is not worth worrying about, not worth spending your mental energy on, reading temperature specifications and doing research about battery chemistry and discharge rates. If the battery begins to fail dramatically for some reason within a year, bring it back to Apple. Otherwise, who cares?

    The whole point of the iPad is that it transforms into whatever you are doing with it, letting you forget that you're dealing with a machine and just get absorbed into the task at hand. Worrying about the thermal design defeats the whole point of the device you paid $500+ for.

    Spend your time worrying about things that matter, not whether you damaged the battery in your gadget by reading in bed for too long.
     
  19. TrimmTrabb thread starter macrumors member

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    Apr 10, 2012
    #19
    Thanks. Those are valid comments. I am indeed interested to learn about the science of this, so it's not just about worrying about my possessions. I enjoy technical details. However, part of the reason I started looking into this was because I was concerned about how hot my iPad had become when I wasn't paying attention to it. In that respect, you're right, and it's a good reminder to lighten up.
     
  20. thelookingglass macrumors 68000

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    #20
    Wow, you're way too diplomatic. :) I would've told the other poster to go pound sand if he's not interested in the thread. I too enjoy understanding the technical details of these things. And, in any event, even if I upgrade in 2-3 years I still want to make sure I take good care of my devices. Many of them end up getting passed down to family members.
     
  21. TrimmTrabb thread starter macrumors member

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    Apr 10, 2012
    #21
    Ha. I would've ignored it if it was juvenile and mean-spirited. But I thought he took the time to compose a well-written post and was actually trying to say something positive. :)

    I'm still just as interested in the topic, but he's right that it's not healthy to dwell on it too much.
     

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