"you hook it upto your battery up front that runs off of your alternator but dont do this unless you have a high output alternator or it will kill it"
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that is VERY dependant on alot of things. i had a guy try using an old autosound 2000 quote against putting in one extra battery because of a human pedaling a generator and them adding batteries until they couldnt pedal. lol same condotion happens when your amp draws more than your alt puts out except now all that power then comes from your battery up front which if its not a deep cycle and its all the way up front it will give of less voltage and you further tax it for eventually starting your car. its a trade off depending on alot of variables including listening habits. i ran two old school wet cell deep cycles off a a ford 90 amp alt for 1 year no problem.