I think the following review of battery life on four major VGA PPC can be taken into account and it's fair enough IMHO since he has the opportunity to test drive all 4 of them. As you can see they're all yield about the same result under full load with Dell x50v being 3 mins shorter (Assuming all PDA has the same battery capacity, which is 1000mAh).
P.S. Sorry the site is in russian, I used systran to read it.