I've got 400-500w a/b and 700-800w class D with a 110A alt. Stock electronics on the high demand side as well. Turbocharged, dual electric radiator fans, fog lights, pwr windows seats brakes etc. Using a 5-6 year old wal-mart battery.
Only wiring upgrade is 8 ga from alt to batt.
Slight dimming at idle w/high-full volume.