add a battery or isolate

Im just wanting to see peoples opinions on just adding a second battery to my car, or adding a battery isolator and then add the second battery?  I have a kicker 1250x1watt amp, and a kicker 900x4 watt amp.  I have a 35 farad stinger hybrid cap, and a regular battery under my hood, and I want to add a second in the trunk.  Thanks!

A second battery without upgrading your alternator is throwing good money after bad. The cap is doing you no good, and an additional battery won't do you any good, either, without a charging source... Once you upgrade your alternator, THEN you can add an identical battery to the rear of your car, (that means AGE, too!) but DON'T USE ANY ISOLATION. Simply wire them in parallel, and be done with the whole thing! Isolation (and a second battery) will provide you with no benefit for your SYSTEM, all it will allow you to do is sit with the car off, and still be able to start the car, even after the system pulls the secondary battery dead. If you are looking for parking lot time, THEN add the isolation, but if you are adding a second battery for system performance, then leave it out.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."