4ga. to back battery?

[cvxsmitty58]

Right now i have a run of 4ga going to my amp from the front battery. within the month i will be getting an aq2200d and i want to run another battery in the back. My question is will it be safe if i run this 4ga to the battery positive and do another run of 4 for the negative (I'm getting a run of 4 for free). What kind of fusing will I need on this wire if it will work. I was planning on grounding the back battery in the back, is this necessary if im running a ground from the front? I have part of the big 3 done and i will definitely finish it before putting the second battery in. Im planning on running 0 or 2 from the back battery to the amp. I will be using the same battery in the back as i have up front.

Thanks guys.

[kl0wn]

If you do run the 4ga, I wouldn't keep it for a while. It will work, but I would upgrade to 0 soon as possible. If you do decide to go ahead and use the 4ga before upgrading, use a 120amp fuse.

The question about grounding the back battery to the frame after already having a run from the front. It is not "needed", but it can't hurt to have a bit of extra flow.