my alternator is a 160 amp one. the stock one is I believe a 90 amp one.
I have the juice from alternator running to a 200 amp battery isolator which charges both batteries(RedTop & Yellowtop) as needed...but the Red Top (starting) is running through the stock cables and charging system.
The YellowTop is running the Winch and the Car amp and never has anyproblems. Both batteries are only less than a year of life.
I used to only get 2-4 hours of stock stereo play, but now I can let it play for about 7-8 hours before it dies.