ViLeGlyph:
This is all really useful information thank you all! I am headed in the right direction now. I will be powering my board of my car battery. I know that its rated for 700 amps cca. But I want variable amperage tolerance on the device so that when I swap my battery I wont have to worry about matching amps. Or does the amperage not matter as long as its greatee than the requirement?
Your car's batter amperage rating is about what the batter can supply, not what it must supply. What matters is how much your particular circuit is drawing. If you are pushing your regulator to provide its maxium current rating of 500ma, then your regulator will be drawing something less than 1A from your car battery, but more than 500ma. The reason is that the regulator is not 100% efficient. That means it consumes some amount of power just to provide power to your circuit.
So short, answer any battery that will start your car, will work fine with powering your circuit.