There are tons of variables that go into battery life - starting with the type and age of the batteries.
I can tell you that I get many, many hours of batteries life with my Eneloops (I have older white and newer black styles). The older the batteries I use, the less times I get. But that's just a start.
I have multiple sets of batteries for my handhelds and at least one set is always being charged.
Other likely factors:
- backlighting: I have the backlight set to high but only lighting during transmissions
- recording: I tend to record everything
- analog vs. digital: I suspect digital voice causes more battery drain than analog; I have a good mix of analog and digital in my typical monitoring
- amount of activity: if the radio is constantly talking, it will certainly wear the batteries down much more quickly than sporadic activity
Anything you can do in these areas can help to extend your battery life. Beyond that, your best bet is to get a couple of good sets of NiMH batteries (I recommend Eneloops), always have one set charging, plug the radio in whenever possible, use the built-in trickle charge* to help keep the batteries charged, and check your backlight settings.
* in the past, I would never use the in radio charger but with the TRX, I use it all the time and have never had a problem.