Recently I happen to replace a new iPhone 4 replacement battery, with a little bit of peel down of the battery, I saw there is a bare lithium battery unit with a PCB battery protection board.

iphone4 internal battery skin peel

My idea is to lead two wires from the input to an external pack of 3 paralleled Panasonic NCR18650A (3100mAh 18650) batteries, totalling battery capacity to around 3.7v 10Ah.

My question is will this work? Charging and Discharging, reasonable accuracy on the percentage of battery capacity measuring? Thanks.

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    \$\begingroup\$ Just looking at the battery on amazon, the reviews are overwhelmingly negative, personally I would be very careful with that for your iPhone. \$\endgroup\$ – ColdestShadow Aug 14 '12 at 17:51
  • \$\begingroup\$ Sorry I used image from this seller. bought from another seller and it is working well for about 1 month. and my hobby would like to have some extra capacity. \$\endgroup\$ – c2h2 Aug 14 '12 at 17:53

Don't bother. Here are the issues:

  1. The circuit you are connecting this to is not going to expect the higher charging current and at best won't know how to behave. At worst it might damage something.

  2. There is software inside the iPhone that tracks the rate of discharge and estimates the remaining power. This software will do some learning, to adjust for battery differences, but it is unlikely to adjust for a 2x or 3x capacity increase.

You would be better off making what is essentially a USB battery pack. A battery that has a USB jack on it so you can plug in various USB devices to charge them. This would be a cleaner design (no weird wires coming out of your iPhone) and would also work with other devices without modification.


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