hmmm, I'd do a couple things. If you are lucky you have a shop that will test your starting and charging system for you out in the parking lot. Using their inductive pickup, you can have them measure current draw during starting. See if it's excessive. (or feel the cable and see if it's hot)
Also, where did you ground it? woops, don't run a ground wire up front. But make sure your frame to engine ground is still connected. There is a ground strap on the lower front passenger side of the engine from the body of the car to the forward motor mount bolt. Make sure that is still there.
And yes, 0 gauge wire would be better. But I don't think it should be necessary.