Just curious how you arrived at this conclusion.
Capacity testing is often done using a C/10 rate. For a 2300 mAh battery, that would be 230 mA.
The battery range used by the phone is 3.6 to 4.2 V, 3.9 V midpoint.
3.9 V / 0.23 A ~ 17 Ohm -- 18 Ohm is the closest 10% tolerance resistor (5% or even 1% is better, but harder to find). 4.2 V -- 233 mA, 3.9 V -- 217 mA. 4.2 V * 0.23 A ~ 1 W
Hook up an 18 Ohm, 1 W (or more) resistor to the battery, it should take about 10 hours to discharge from 4.2 V to 3.6 V. (Do this out of the phone, with a voltmeter.)
Be warned that the resistor will get hot in the process!
If you get ~ 10 hours, then it is believably a 2300 mAh battery. If you get less than ~9 hours (10% tolerance resistor, plus the approximation of constant load), then it probably isn't a 2300mAh battery, at least under C/10 rating.