Overdischarged iPhone battery

Discussion in 'General Electronics Chat' started by Russell_AH, Jul 4, 2013.

  1. Russell_AH

    Thread Starter New Member

    Mar 29, 2013
    Hi all, I've been having a problem with my iPhone 3gs, and I am wondering if I may have overdischarged the battery.

    Basically I was using the phone while it was low on battery, and instead of shutting itself down at around 4% battery life it held out till 1% before shutting down. Since then I have not been able to charge it (tried cleaning the socket, different cables etc).

    I had thought it may have been the docking port that was broken, but considering the circumstances I had a look at the battery.

    I've attached a diagram containing the 4 connectors on the battery. The voltages I measured are:
    A-B: 2.16V
    A-C and A-D: 0.17 V
    C-D: 0V
    C-B and D-B: 1.95V

    I’d guess that A and B are the main power contacts, with C and D performing other functions (https://discussions.apple.com/thread/2744613?start=0&tstart=0). The fact that I’m only getting 2.16V is a bit worrying (making me think I’ve over discharged the battery).

    According to here (http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries) the battery may have shut itself down (so won’t be recharged), but it could be saved as the voltage is above 1.5V.

    My main questions are:

    Do any of you have any input on my diagnosis?

    And any ideas how I would go about recharging the battery? I don’t have a charger, but I do have various electronics bits and a microcontroller, so might be able to cobble something together if I knew what to make.

    If it makes much difference, the battery is a Lithium-ion polymer battery (3.7V, 4.51Whr).
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Those batteries are supposed to have internal circuitry that opens up when the battery is too low to prevent over discharge damage. The battery may simply be bad. They do have a life span and are made by humans which means some are simply defective. The other possibility is it has circuitry that "commits suicide" if it detects a failed battery. Li-Poly cells are potentially dangerous.

    That is the chemistry that can catch fire if over charged so it's not a good idea to mess around with charging the cells directly.
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    You can buy a new battery on eBay for $10. It will include a special screw driver to open the case. The whole process of changing the battery takes about 10 minutes. That should hold you over until the next generation of iPhone is available.