If you have your phone set to automatically sync email accounts, that's one more place where it will use a significant amount of battery, as it checks frequently. Ideally, any app that syncs over the web should be set to manually update if you want to save some battery life. Also, whenever possible, do any syncing/updating of apps when on wifi, as doing so on a data connection uses more battery than doing so over wifi, because it takes longer to do so.
As far as what was mentioned about warranty, I wouldn't be surprised if a standard warranty does not cover the battery for the entire period either. This has been my experience with other electronics such as laptops, where say, a laptop has a 1 year warranty, but the battery itself is only covered for 6 months. My Ascend seems to have gotten worse on battery usage over the last few months as well, and I've had it for nearly a year, so that battery may very well be on its way out. Your only real option is to keep your charger on hand, and if you're in the car a lot, get a car charger. You can get an aftermarket car charger that plugs into the cigarette lighter/power port in your car and has 1-2 USB slots for 10-15 bucks, depending on where you buy it. I find this to be a better solution than a dedicated car charger, because I can use my USB cable with the wall charger, the PC, and in the car, and don't have to buy additional cables.