Revamped version of the iPhone 3G with faster processing speeds. Repair of this device is similar to the 3G, and requires simple screwdrivers and prying tools. Model A1303 / 16 or 32 GB capacity / black or white plastic back.

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Battery: test for proper voltage?

I have a iPhone 3GS that won't power on, I have it all torn apart and have the battery out. How can I test the battery with a multimeter to make sure it has a charge. Also I hear there is a way to use exposed wires on a usb wire to charge the battery?

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The outer two contacts are the main battery contacts - you should read about 3.7 volts across them. The inner two contacts are for current monitoring (I think) as they only have small conductors.

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Hi, i think my battery is faulty, between the two outer contacts, it reads 0.12v

i think its clear that it needs changing, ?



yes it does, it might even need replacing. Also remember that the battery may be discharged to a point that you USB will not charge it, try an AC adapter and there is also a trick in giving it a bit of extra charge to awaken the charge circuit.


Hi, thanks for the info

I have ordered a new battery on eBay, i will change it and see what happens



Hello i'm an electronics technician expert! You must know that a full charge of a 3.7volt battery will give you around 4.1~4.0 volts when you measure it.

;) SO a full charged battery IS NOT ONLY 3.7volts. :D .


I do not see where anybody said that a fully charged battery is 3.7volts...:-)


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A couple of points here from a design engineer of 30 years. On charge (and fully charged) a LiPo (Lithium Polymer) battery should have about 4.20 - 4.30V across its terminals. With the charger freshly switched off the voltage will be about 4.1V. When fully discharged the battery voltage can be as low as 2.7V. Any lower than that and the battery is permanently dead! That's why most LiPo batteries have overdischarge cutout built in.

As for Jonathan's Amps, if you short out the iPhone battery (or connect your multimeter across it set to measure current) I would expect TENS of Amps to flow. This is a bad idea! Never connect a multimeter across a battery when set to measure Amps. The ability of a battery to supply current is not related to the capacity of the charger.

Measuring voltage is fine, but as Jonathan correctly points out it tells you nothing about the Amp-Hour capacity of the battery. To measure this you need to take a known current out of the battery and measure the time taken for the battery to reach end voltage (2.7-2-9V). Amp - Hours is exactly that, Amps(load) x Hours (Time).

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Volts tested do not give indication of battery quality. (confirmed) I bought a new battery off ebay and found I was experiencing the same low battery symptoms with my iphone that I had with the old battery. I tested the voltage of both batteries after a full charge and got 4volts *and 8.5 to 9 amps*. (*Correction I don't know what I'm talking about in regards to amps. SOrry.*) After taking the phone to the technicians it turns out the batteries were no good. Next time I have my phone apart I'll check the amps on the new battery. Any ideas how many amps a new battery should read?

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Jonathan, you are certain you get 8.5 to 9 amps out of an iPhone battery? ;-)


Jonathan, I believe that the iPhone battery is a 3.7Volt 1200mAh battery. That means it can supply 1200 milliamps (1amp) of energy at 3.7V for one hour. The USB charges your battery at 500mAh and the AC adapter at 1A. It would be quite an engineering accomplishment to obtain 8.5 to 9 amps from that battery. However, you are right, the voltage measurement is not an indication of the overall condition of the battery.


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