I have a sony sj22, and while it doesn't have sound or as fast a processor- it does have hires screen (the biggest battery drainer).
If you lose 20% of your battery in 90 mins then there MAY be something wrong. However, check to make sure the brightness wasn't All the way up (unnecessary and wasteful). I use the default launcher cause I like it, the small battery advantages are nice too
try it for a few more days, and if it doesn't get better return it asap. Crappy battery life will drive u insane, which is why I went w/ Palm instead of ppc.