I've seen the battery of my N900 perform like this:

• When using the default kernel and only GSM, no data connection of any kind and not doing anything on the N900, except for a few calls it lasts 4 days
• Like above, but adding around 30 minutes of wi-fi per day, it lasts 2 days
• Like above, but adding more wifi (total 1 hour per day, not continous), it lasts one day.

In general, if I stay a while (from 30 min to 1 hour) reading something or playing, the battery lasts just one day.

After upgrading the kernel to Titan's power kernel, but without any kind of overclocking (default settings), the max time I get is 2,5 days.

If I use the MStarDict application and forget to close it, the battery drains in a few hours.