For starters I have had my battery in my Telrad for three years, and once left it on for a week, with a Telrad it is a Zero mag finder , when used in conjunction with a Star Chart, helps you navigate your way around the sky.
A finder scope is usualy an 8x30 to 8x50 mag and is for when you get closer to the object you are looking for , but sometimes the object is fainter than the finderscope is able to see,but you check the star patterns against the star chart.
There is no problem mounting a finderscope or a Telrad on your 12" scope.
I hope this helps
