Steve
Have you got a copy of Bob Nuckolls  Book? Along with Tracy's diagrams in his ec2/3 manual you'll have all the infomation you require

What alternator are you using? I ended up using a 60 or 70 amp unit out of a subaru and converted it to external regulation as the 100amp unit that came with the renesis was going to be a real bugger to make work. cannot remember the details now but at the time it seemed like half the regulator was in the alt and half in the cars EC(which I didn't have).

My 2c opinion is that the Alternator is the main source of power, the battery is a backup. so battery should be sized to suit your desired Alternator off endurance, which will be specific to your aircrafts minimum electric power consumption. If your ever planing on flying east or up north from Perth I'd suggest to try for 3-4 hours battery endurance just to make sure you can safely make a landing area near civilization.

Andrew Martin