I have read that a "rewound alternator or a second dry cell battery w/an isolater" or a capacitor may be needed when adding amplifiers to a car audio system in order to supply the amplifiers with sufficient power. How do you determine your power needs before the install? I am thinking of adding two amplifiers, one for the sub and one for the rest of the system. Probably a JL Audio amp, but I'm not sure. I want a high quality amplifier.