so im tossing the idea of a multi battery set up for my truck just a few questions:

so if i use an isolator can i buy an isolator rated for a 200 amp alternator and use it on my stock alternator i beleive only 70 amps?
or can you only use the isolator rated for the output of my alternator?

im thinking that i want to run 3 batteries one to run the bare minimums and then join the other two cause ill have a winch and a bunch of lights running off of them. i know the winch draws alot of power and so will the lights cause i fore see me useing them lots.
or to run one battery to run the bare minimums then to seperate the other two to run my lights an winch. is there a way to connect the two batteries so that the winch draws from both batteries but the lights dont draw from both?

 

Are you talking about 2 12 volt battery's? that's 24 volts and you will fry things.

I have a dual battery set up with a isolator and stock alternator I run the stock equipment from the stock side battery and a 1600 watt stereo with 10 speakers , 8 130 watt lights 4 back up lights 55 watts each and a winch from the second battery with no issues.

most of the time you will not be running everything at the same time anyway so you will have plenty of battery to run your accessory's single or in almost any multi combination with just a second battery and isolator no need to over engineer the battery set up.

 

Although you can safely connect two 12V batteries together to give you only 12V out (parallel connection instead of the series connection you are thinking about that would give you 24V), I agree that two aux batteries are a bit overkill for what you are doing. Get 1 good high capacity deep cycle battery to use as your aux battery, and keep your stock battery for stock loads.

And yes, you can use an isolator that's rated at higher current than what your alternator puts out.