3 Replies Latest reply: Jul 19, 2012 10:39 AM by cudaboy_71
RobertThePro Level 1 Level 1 (0 points)

What is the iPhone 4 Battery Capacity?

iFixIt says "3.7V 1420 mAh Li-Polymer battery" is this correct?
If i have a 1900 mAh chrager for the iPhone how much will it charge my iPhone?


iPhone 4, iOS 4.3.2
  • 1. Re: iPhone 4 Battery Capacity
    cudaboy_71 Level 1 Level 1 (135 points)

    It doesn't quite work like that. the mAh of the charger indicates the RATE at which it puts current back in and has no bearing on how fully it charges the pack. It will completely charge the cell. Provided this is a proper iPhone charger (meaning it is a lithium cell charger and NOT a NiMH or NiCD charger), using its on-board circuity, the charger will completely charge the battery at a rate not to exceed the label (1900mAh).

     

    This might bear a little further explanation. First, lithium cells can not be effectively charged at a constant rate. The on-board circutry monitors several factors and ramps up or down the rate accordingly (or poof--smoke--fire). So, the fact that the charger is a 1900mAh variety, it will not charge at this rate the whole time--it will simply not apply more charge than that rate. So, you might be tempted to divide 1420 by 1900 and assume that you'd acheive full charge in 74.7% of an hour, or ~44 minutes. But, this is not accurate due to the up and down ramps of input current.

     

    The other thing that might bear discussion i the maximum charge rate. That rate is commonly discussed in values of "C" or Capacity. A 1420mah cell has a 1C of 1420mah. Or, to look at it in terms of this specific charger you would be charging the cell at 1.33C. As a matter of typical charge rates for lithium polymer cells, 1C is a good, safe rate. Over the past 18-24 months however lithium polymer technology has allowed for the use of higher C charging. In some applications--using properly specified cells--rates as high as 5C (or 7100mah in the case of a 1420mAh cell) can be safely used.

     

    However, since Apple does not list the recharge C rating in their specs I always default personally to 1C rates (and, yes I'd think 1.33C of the 1900mah charger would be ok...YMMV). I say this only to make the point that buying a 3300mah charger to speed up the charging process has two nasty side effects:

     

    1) the potential for fire, if the cell is not rated for high-C charging

    2) regardless of the rating of the cell, higher C charging ALWAYS trades lifetime of cycles for speed. In other words, if you'd get 100 full cycles at 1C, you might only get 60 full cycles at 3C (just pulled those figures from thin air to make the point). Suffice to say, if you have the time (for example overnight charging) the lower the charge rate, the better for the life of your cell.

     

    hope that sheds some light on the topic.

  • 2. Re: iPhone 4 Battery Capacity
    offyonder Level 1 Level 1 (0 points)

    Great explanation. I'm working on getting my head around this without an electrical engineering degree.

     

    I have the Brunton Restore solar charger. Solar aside, the battery in the charger claims a lithium battery that has:

    1) 1,000 mA output to charge devices faster (what is described as the RATE above)

    2) 2,200 mAh battery to charge devices more times

     

    This makes it sound like the mA rating is the speed (rate) that it charges and the mAh rating is the capacity of the battery.

     

    This sounds like it counters what was said above as there is no mention of mA just mAh.

     

    I'm not too worried about how fast it charges (rate) but more with how much charge I can get.

     

    If the iPhone 4 battery is a 1420 mAh battery, should I be able to charge it about 1.5 times with a 2,200 mAh battery?

     

    Thanks!

  • 3. Re: iPhone 4 Battery Capacity
    cudaboy_71 Level 1 Level 1 (135 points)

    apologies. after rereading my post, i see i mixed (rather neglected) the terms. you are correct: mA is the term for rate, and mAh is the term for capacity. I hope that bit of info makes my post make more sense.

     

    So, the specs of your Brunton Restore charger indicate:

     

    1) that it will charge at a 1Ah rate (1000mA = 1Ah), or 1C for a 1000 mAh cell. For the 1420mAh iPhone battery this is well below the 1C charge rate. Or, a good safe (if not as quickly charging as possible) rate. This, regardless of the capacity of the cell in the recharger. It could have a 9000mAh store and you'd still only charge at .7C. Of course, that charger would weigh a few pounds and be the size of a full size external hard drive.

     

    2) Yes, 2,200 mAh capacity of the Restore charger indicates the ability to fill that 1420mAh cell more times. However, the 1.5 times figure may not be completely accurate. Lithium cells (unlike alkeline, Nimh, Nicd) can NOT be completely depleted without damaging the cell. Therefore, "depletion" (indicated by 0% on the device) is actually more like an 80% depleted cell. It's hard to nail down "depleted" because the circuitry signals off of cell voltage--usually around 3.0v. The actual capacity of the pack remaining is really an unknown. But, for the sake of argument, lets just say a complete cycle of a lithium cell is 80% of the total capacity--that 1420mah pack really only requires 1136mAh to recharge. So, you'd really get more like two complete recharges using the Brunton Restore (1.94 times using the 80% figure). YMMV.

     

    Hope that helps.