yeah what the other fellows said, volts is whats usually tested here, CCA on the battery means of course, cold cranking amps and it is a spec that the manufacturer of the car says is the minimum the battery needs to be able to output when you buy it. But if you are testing it the rule of thumb is for volts.
Desired voltage, engine idling (give it two minutes to recharge from the start): 13.9 - 15.0 volts
Battery, engine off: desired, 12.8 - 13.0
marginal: 12.4 - 12.7
That all makes sense, most of that I knew. I have a voltmeter gauge on my A-pillar and the voltage is fine. The reason I'm asking is I'm looking at upgrading my alternator. The one I'm looking at says at idle it puts out 115amps (200 amps overall). I know our stock alternator is ~80amps but I doubt its 80 amps at idle. Any comments? Thanks for all the responses though. Much appreciated.
What they are saying is that their alternator is CAPABLE of producing that current at idle, should the system indicate to the regulator that such current is needed. A car with a very large sound system and electric hydraulics might need that kind of power for parking lot tricks. Other vehicles like ambulances also use high output alternators to power all of the lights and equipment while working on-scene.
If you don't need a high output at idle, there's no reason to buy one.