SInce I don't have a 900 I don't know how helpful this will be but from my 800 I have learned to set the refresh time on the rss reader and anything else that needs to update to at least twice what the default is.

Also I check modest from time to time to see if it choked, which it does often, which can lead to battery drain. And occasionally browserd will duplicate itself and eat battery. I think fennec (firefox) is "browserd" now so that may not be an issue.

So generally I'd suggest checking the update intervals. Also since this is now a phone, if you're in a spot with poor cell reception your battery is going to get drained because the phone is trying to reach the cell tower more frequently (or whatever it does in poor reception conditions). That alone kills the battery on my chinese iPhone knock off in 24 hours even when I've not used the thing.