Faulty iPhone 4S battery - how can I test a battery to measure its integrity?
I have always liked to test a battery by running the device until it shuts down and powers off.

When you connect it to the standard wall charger, it should take between 2 and 4 hours to charge. If your battery is done charging in an hour to 1:30, then it's not really getting the intended amount of current and should be replaced.

Similarly, if it won't charge fully (or very much close to full) in less than 4 hours - something also is amiss either with the charging, measuring or battery itself.

By timing the charge time, you eliminate any background task, GPS, WiFi drain, etc.. and just can see the time it takes a fixed amount of current to enter the battery and be stored chemically.