Let's Make Robots!

how do i monitor power useing Analogue I/P's

Hi Everyone, I have a 28x2 picaxe. I want to be able to monitor two different battery power packs (approx 5v each) on two of the analogue inputs. This is so I can switch to the best one using a relay on one of the outputs to power the Robot. I will use a time OFF delay with a capacitor so the picaxe is still powered during switchover.

My question is what circuit can give me the decline values into the Analogue input.???

Anyone help?

Vinny