Unlike a laptop (which has fairly consistent discharge rates) your touch pro (and every HTC phone I've ever owned, this is the 4th model) is literally all over the map for use. It's a lot more like a car. You can idle in your driveway for hours on half a gallon of gas, but if you put your foot down and keep it down you'll be all done with that gas in a few minutes.
I use this rule of thumb for myself, based on the stock 1340Mah battery and the following ballpark drawing rates
* standby: 30ma or 2%/hour - this is doing NOTHING AT ALL but not powered off - you can receive calls and txts
- can go a couple days doing nothing
* on, backlight, but not surfing (ie, using as a PDA, music but NOT video..., PIM): 170ma or 12%/hour - about 8 hours total
* anything using a data radio - wifi, surfing, gps: 500ma or 33%/hour ( 3 hours total)
* watching video is about the same as data use above (yep 3 hours)
* voice: 350ma or about 25%/hour (4 hours talk time with a very good signal and backlight off)
So, 3-4 hours talk, < 3 hour data, 8 or so of using computer/pda features.
So if you look at your battery and its at 50%, if you did nothing it would last a day. If you talk, it's good for 2 hours. Surf for about 1:30.
Unfortunately it has no way of knowing what you're going to do to it, so you have to be the computer