What sort of battery life do you get? 2g Jailbroken on 3.0

[piblondin]

I recently got a new 2g iPhone as a replacement from the Apple Store, and the battery life just seems awful. I'm getting just under 4 hours of usage on a single charge (as shown under Settings-->General-->Usage). What are other people getting? I would like to know so I can determine whether I should have one of my friends with an AT&T SIM card take it back while it's still under warranty to get another new phone.

Thanks!