Alternators don't put out more than 90 to 130 watts (average) and even then that number is skewed because the alternator will output at 14.4 volts (optimal) meaning the watts are actually lower than that reported at 12.The starter is like 90% of the reason for the battery. The starter uses a huge amount of amperage to TURN AN ENGINE. If you don't know how hard this is then next time your serpentine/fan belt is off just TRY to turn that thing by hand. The starter is also why you use wet cell batteries. A dry cell that produces that many amps would be really big and have a lot of internal resistance.