Questions for battery relocation
 

What size of positive terminal wire should I use?
Is 2-guage wire strong enough?
Do I need to run the negative wire too, or just ground it to the trunk?
How many fuse do I need for the positive wire, one at each end, or only one at the battery end?

Thanks and regards,

Sammy

Run both power and ground, use a minimum of 2 gauge wire. Use a fuse at each end of the power wire. There is ample room to run the new wiring through the firewall from behind the windshield washer resevoir. You cannot use the existing battery inside of the vehicle, you will need to go to a Optima type battery that does not produce gas.

Thanks forbidden for your inputs. I have the Optima yellow top. Is there any specific reason for running the negative wire also?

Read the grounding sticky.

Even an AGM battery like Optima can still produce hydrogen gas. It is much less during normal operation but still there. BUT if the battery becomes shorted or charging system overcharges for some reason, it WILL vent a lot! The 2 dark porous-looking buttons are where the vents are. The original Miata battery was an AGM but since it was in an enclosed space in the trunk, venting was still provided for this reason. I would strongly suggest your fabrication include a way to make sure any vented gas does not accumulate in the trunk. E.g., a sealed battery-box with vent tubes to the outside.

Wouldn't it make more sense to run the shortest ground possible and just ground both ends to the chassis. Also how many amps does it take to crank the car, wouldn't 4awg be sufficent? And in that case what size fuses. Sorry for the thread hijack but i was also wondering about that resistor or fuse on that plastic piece on the pos. terminal can that whole part be replaced with something else?

Honestly I can't see any benefits worth the trouble, unless your doing some kind of show car setup. I think that you can get just as good results by running a power and a ground to the battery where it is now and have a nice capacitor in the trunk...

but of course, I'm not an electrical engineer.

Well the idea of running a ground that distance just doesn't make sense to me. The shorter the wire the lower the resistance and the better the ground. With a turbo or sc setup that added space under the hood sure could help and could probably help with cooling as well.

I can say from experience that you don't need to run the ground wire, a good chassis grounding at both ends will be more than sufficient. Also, 4g wire is strong enough to start my car, and run the 1000 watts of stereo sitting in the trunk right now with the battery. Best advice I can give is make sure that the battery is secured to the chassis solidly, things tend to move around quite easily in there.