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?
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?
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).