two batteries to alternator

Im new to the forum and i am wondering how to wire another battery to my alternator so that its not pulling too much from my main battery for the car electronic system? I have a 20 Farad Capacitor and feel like im putting too much strain on the car.

wire it in parallel with your front battery and fuse each end of the power wire between the batteries

You may not need a second battery. You are worried about loading down your electrical system, well a second battery is another load!

1: aznboi is right, parallel the connections, positive to positive, with TWO fuses between them, (rated for the capacity of the wire, and no larger) one within 18 inches of each end, BUT the batteries must both be a: same AGE, b: same KIND (i.e. brand and contruction technology), and c: same CAPACITY, or you will end up replacing them both sooner than necessary.

2: audiocableguy is ALSO right. What is your situation, that we might be able to give you some more insight... A second battery, once fully charged, is an exceptionally MINOR additional load (about 1-2A for "maintenance charge"), when discharged to the same level as the front battery, it can become quite a significant additional load (conceiveably, up to 100A or even more, if the discharge is deep enough).

I expect you are chasing the wrong cat! I think your answer lies NOT in a second battery, but in a larger alternator, THE SOURCE of all power in a car. Think of it like this:

Say you have a fire hydrant, attached to the city's water system, and you are trying to put out a huge fire (this will be the analog of your amplifier and car's accessories), and the amount of water required to douse this fire amounts to 1000 gallons per minute, but you are getting all of the 1000 gallons per minute from one hydrant - the battery in your car. Sure, it's going to keep up for a little while, but read on.

Now, the city's water system (the ALTERNATOR in your car) can only SUPPLY 500 gallons per minute. What's gonna happen? That's right. The fire (or your accessories) is going to win this battle.

If your alternator is too small, a second battery (imagine a second hydrant) is NOT going to help! All a second battery will do is cause BOTH batteries to recover more slowly. You still only have 500 gallons per minute! (as it were) You probably need an alternator, plain and simple. You've already discovered that the cap isn't doing you any good, and it never will, until you upgrade the alternator... but even then, the benefits are both minor and debatable.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."