I'm baffled. After doing some mior research, I found that charging the iPhone 4 with a cable/plug other than the supplied one result is decreased battery charge. I have been doing this since I got my iPhone 4, 'cause I already have one lying around. Since then, I have been getting an average 5 hours of usage a day before my phone goes down to around 20 to 25%. I thought this is not normal so I tried using the supplied cable and charged my phone overnight. This morning, I noticed that my phone stayed at 100% and never dropped to 99% until after 16 minutes of usage (better than the usual I think). At this rate, I might just hit 25 hours of usage before my phone needs a recharge. Have anybody else notice this?