1. Battery gauge accuracy out-of-the-box. Your battery gauge will not have been calibrated until you've done 2 or 3 complete charge/discharge cycles (100% to 0%). Until calibrated, it might be reporting 20% when there's a lot more run time left in the battery. (But don't deep cycle calibrate too often as this will shorten the battery life). 2. Active Data and Voice usage. Apple engineers have said that this is the activity that drains the battery at the highest rate. 3. Application use. One guess is that battery life under continuous (non-game, non-network) use is only about 6 to 8 hours. Games that use the graphics chip may drain the battery even faster. Applications that use the network will drain the battery even faster. 4. 3G cell tower proximity. If you are far from a 3G tower, or don't get many bars, the iPhone transmitter power will get turned up. This can consume a lot of power, both in standby and when used for voice/data. Try testing in two different locations known to be near/far from a 3G cell phone tower. (How does one determine that?) Or if you are near an EDGE tower, try turning 3G off. 5. Backlight Brightness (in Settings) : Please report your backlight brightness. This makes a big difference in battery life on other handheld devices. 6. Push Data: (suspected) Has anyone actually measured the difference in standby battery life (after after calibration) of keeping Push data ON/OFF? 7. Location Services: (suspected) Has anyone actually measured the difference in standby battery life (after battery calibration) of keeping the GPS chip ON/OFF? 8. wifi: (suspected) Has anyone actually measured the difference in standby battery life (after battery calibration) of keeping wifi ON/OFF? Also, wifi power usage will vary with distance from the access point. Try turning wifi off if you aren't getting any usable wifi bars, else the iPhone will just waste power trying to connect.