560x vs. 560z in battery life

[Foxhound]

I was thinking of going to a 560z from a 560x (I just love the laptop for some reason, I don't know why, but, the form factor amazes me). I don't have enough money to plunge for a new laptop, but, have found myself building up the older thinkpads.
I was just wondering, does anyone know how much worse the battery life would be on a 560z? I've got 4 old batteries here, of varying life time (one woks for 2 hours on my 560x, two only 30~45 minutes...)
I don't really need it to last any more than an hour and a bit, but, more is always welcome. I am guessing there might be more CPU speed scaling features on the pentium 2 as well (there are none at all on the 560x as far as I can tell).