Here's some details on my battery relocation for a future turbo setup. My goal was to have the battery fit behind the LHS rear glove box, which it does. The pictures show the actual cable route that fits under the carpet inside the car. I used grommets at the passenger footwell where the cables pass through the chassis.

I ran both positive and negative 2/0 gauge welding cable to relocate the battery to the drivers rear side for the turbo. The cable weighs about 40lbs cable. I soldered on copper lugs to each end. The negative cable runs right to the front RHS of the cylinder head, with a 2Ga cable back to the RHS fender harness ground bolt. Positive runs to a junction block behind the RHS headlight, then same 2/0Ga to the starter.

The wiring runs down the inside passenger side and right beside the PCM bundle that passes through the fender. I decided to install grounded metal braid covering that is grounded to the frame to prevent any interference that *may* get created and mess with engine sensor signals to the PCM. The braid is from McMaster Carr #5537K28 [Super-Abrasion-Resistant Expandable Sleeving Interference Shielding Metal, 25/32" ID]. It would be a bitch to trace something like that.

I picked up a battery tray from a 78-83 Malibu (also fits others), Goodmark #4035-300-78 from Summit for $35. It uses the stock F-body battery hold-down plastic thing and bolt and will be nice and clean. The tray did need to be narrowed about an inch each side to fit. I have it bolted at the back corner to the inner fender and through the floor at 2 places.
I do know this setup is not NHRA legal as the battery is not in an approved box or behind a firewall, but it's fine for my street use.

The battery has 2 vent ports built right in that the silicone tubing connect (push) on to so it safely vents outside the car. The battery is the standard one for the car, nothing special.

 

Nice job!

 

I realize this is an older thread but i went this route with my car and just wanted to add that a 70-81 F-Body battery tray can also be used. This clears with no problem and gives you a 78 series size battery for just a little more CCA