Thanks @peter.jeffery.nz,
I entered your figures into a table with dates as they reach each voltage and did some calculations to help me to forecast when to change the batteries. Prior to my first set of alkaline batteries I didnt know how sudden the drop would be at the end. Now knowing the end droop I reckon for time planning purposes it is useful to note the number of days available between 2.4V and 2.0V. Your Sky2 had 20 days where as my Sky (with 6/8 batteries working) had 16 days, which makes sense.
cheers Ian 