The latest AIRs - those with the little dome on the front face of the reg - are capable of being setup for lower pressure usage.
You shouldn't need to do this though, since, as everybody has said, your front reg drops the AIR output to the working pressure of your cocker. The ability for the latest AIRs to operate at low pressure only become important if you don't use a second reg.
Personally, I like to set my AIR to 700 for my Racegun, it helps ensure that there's enough air flowing during rapid fire.
As for the batteries going flat, did any of you have silver (ie. polished aluminium) AIRs by any chance? There was a problem discovered with these where the batteries were shorting out thus draining very quickly & WDP produced a shield to stop this occuring. As a note, I've got an AIR that was one of the first out - and I mean first, WDP had us finish building them on the tech course - and it's still using the same battery.