Are you using a hybrid OS?On an average-use day, my 9800 uses less than 1% per hour. If I have to stretch the battery out, I can make almost 4 days draining it down to 10%. On a heavy-use day with lots of OWA-mail use and phone calls it will use between 2 and 2.5% per hour giving me 2 days of use.
My first battery lasted me 18 months before it started to give out and needed to be replaced.