When is a second alternater adviseable? I have the single, and wondered why it was such a desireable thing.

When you start needing more amperage because you've added alot of electrical accessories like; TVs, big amps and speakers, air compressor, power inverter or in my case 600 watts of lights on a lightbar. I can have my seat heater on, rear defost on, regular lights on and fire up my 6 added on lights, my volt guage (even at idle) never moves from 14v, plus I can still charge my RV while towing.

But really, its only needed in extreme circumstances.

yes