I've been reading a lot of posts and articles on how to save the battery life on iPhone 3GS. I rarely got through the day without having to charge the battery during the day. I usually got about 5~6 hours of usage with about 12~13 good hours of battery life, but was hesitant on turning off any features on the iPhone. For example, turning down the brightness or turning off 3G didn't change much in the battery life. I now have most of the features on during the day. Except for Location Services until I need it. My screen brightness is set to 100%, fetch every 15 minutes, use push for applications and emails that is capable of push. I do use WiFi when there's one available, but the location services was the big change. I now go through the day and still have 30~40% of battery available before putting it in a charger before going to bed. That's about 5~6 hours of usage with about 15 hours of standby. That's good enough for me, since I never expect the iPhone to last a few days like my previous regular cell phones did. It is a smartphone, and if it can last one day, I'm happy. Try turning off location services until you need it, if you have issues with 3GS battery life.. That will be a big difference.