Battery consumption of Pic18

hi,

I am designing a data acquisition model using PIC18 (20MHz). I wonder, if i use 9V batteries as voltage source, how long it can supply the voltage?

It depends on the maH rating of the battery, obviously not all batteries are the same, a alkaline will last much longer then a normal one...

But let's say a standard varta 9V alkaline: 500mAH, and a pic wch draws somewhere between 3 and 5mA at 20mHz, that's about 100 hours

that is, ofcourse, for the pic only. Normally you will have some other components besides the pic (the pic is controlling someting, right?)...
This will use power too ...