It may be time to show this again.....

Battery Relocation:
First of all, why would you want to move the battery from its stock location? Well, in the case of a ricer, you may need the room for an aftermarket intake pipe or in the case of a rear-drive car, you may want to improve the front/rear weight distribution and put more weight on the rear tires. Now, a front motor, rear drive car twists the frame under acceleration in such a manner that the left front gets lighter, the right front gets heavier, the left rear gets heavier and the right rear gets lighter. That's why you see so many worn-out right rear tires on a car with a one-legger (open, non-posi) differential and the driver "peelin' rubber" at every opportunity. The left rear bites because it has more weight on it and the lightly-loaded right tire spins. Even if you have a posi or a spool, doesn't it make sense to try to equalize the weight on both rear tires so the system can work more efficiently? So if you're going to move the battery, it makes sense to mount it in the extreme right rear corner of the car, no matter if the diff is open, posi or spool.

Now that the new position is nailed down, let's address some of the NHRA requirements to make it work by the rules. The main things we're concerned with in an incident is keeping battery acid off the driver and also making certain the battery stays secured in the car. Here, I'll quote the rule on batteries from Section 8:1 under General Regulations in the 2005 NHRA Rulebook:
8.1 BATTERIES
All batteries must be securely mounted. Batteries may not be relocated into the driver or passenger compartments. Rear firewall of 0.024" steel or 0.032" aluminum (including package tray) required when battery is relocated in trunk. In lieu of a rear firewall, battery may be located in a sealed 0.024" steel or 0.032" aluminum or NHRA-accepted poly box. If sealed box is used in lieu of rear firewall, box may not be used to secure battery and must be vented outside of body. Relocated battery(s) must be fastened to frame or frame structure with a minimum of two 3/8-inch diameter bolts. (J-hooks prohibited or must have open end welded shut.) Metal battery hold-down straps mandatory. Strapping tape prohibited. A maximum of two automobile batteries, or 150 pounds combined maximum weight (unless otherwise specified in Class Requirements), is permitted. Maximums may vary according to class requirements.

Let's examine the rule.
A. Batteries must be securely mounted. No question there.
B. No battery in driver's compartment. What about a hatchback car? Well, technically, the rear of the car on the inside is a package compartment, not a driver's compartment. We pass cars all the time with batteries in this location, but we're pretty darned picky about everything being properly engineered. You can construct a metal bulkhead in one of these cars if you're bull-headed, but it's a lot easier and cleaner to mount the battery in a sealed box in the right rear corner. The one exception to the battery in the driver's compartment is the early VW bug with the OEM battery under the rear bottom seat cushion. If it's a stock bug, I don't say anything about it other than to make sure it's secured, but if the seat cushions are removed and the battery is visibly open to the driver, we've got to start talking sealed box.
C. Rear firewall (car with a trunk). If you're going to start cutting up sheet metal for a firewall, the easiest way is to make a template from heavy construction paper, butcher's paper or light cardboard and transfer the pattern to your sheet metal to be cut. This firewall has to be water tight (package tray too). The material can be secured to the "X" braces with pop rivets or sheet metal screws. These firewalls are tested by one guy shining a flashlight from the trunk of the car and another guy looking into the interior of the car to determine if any light is coming through. The best thing to do is to go to church before you start this project. Again, the common sense thing to do is put the battery in a sealed box and be done with it.
D. Box may not be used to secure battery and must be vented to outside. You want to secure the battery to the car, then cover the battery with the box and secure the box to the car. Run a vent line (a small rubber hose will do) from inside the box to outside the car (through the floor) so there is no buildup of hydrogen gas in the box from the battery being charged.
E. Battery fastened to frame or frame structure. Now, this is ME talking and not the NHRA, but I don't enforce this rule until the car is quick enough to require a roll bar (11.49). Slower than that, it is my opinion that if the battery is properly secured to the floor with the procedure that I'll explain shortly, it's not goin' anywhere. Most of the kids who show up with these slower cars don't have the welding/fabricating skills or tools to do it themselves or the money to pay a pro shop to fabricate the pieces necessary to mount the battery to the frame or frame structure. On the other hand, if he has the wherewithall/expertise to install a roll bar, then he certainly has the means to mount the battery(s) according to the rules.
Here's my logic for fudgin' a little and givin' these youngsters a break...
1. When the battery was in the original position, it wasn't mounted to the frame, it was in a tray which was spot-welded to the firewall or fenderwell sheet metal.
2. NHRA allows a 5-point roll bar in a unibody car to be welded to 6" x 6" plates which are then either welded or bolted to the sheetmetal of the floor. 5 of these plates have a total surface area of 180 square inches. In a 3,000 lb. car, that's a load of about 17 lbs/sq in. if the car is on its lid. Using the same math, a 50 lb. battery would need slightly less than 3 sq in of support on the floor.
F. Minimum of two 3/8-inch diameter bolts. What I suggest using is 3/8" allthread. You can pick up a 2 or 3 ft. stick of it at the hardware for less than 5 bucks and cut it to the length you need. It's easier than trying to locate 3/8" bolts of the proper length. Don't even think about using J-hooks, they are the cheeziest of the cheezy. I do not agree with rule that allows J-hooks if the ends are welded shut. Even at that, the only thing holding the battery in the vehicle is two thin slivers of sheet metal on the tray where the J-hooks go through. Position your battery where you want it and drill a 3/8" hole through the floor on each side. CAUTION: THERE MIGHT BE A GAS TANK UNDER WHERE YOU'RE DRILLING . You'll need 2 locknuts and 2 nice big flat washers at least 1/8" thick under the floor (like fender washers except thicker, or use several fender washers and stack them so they're good and strong and won't "cup-up" and pull through the floor). Use 2 lock nuts with the same large diameter flat washers on top of the floor, tightened to "sandwich" the floor and keep the allthread in place. Using 2 washers of 2" O.D. will give over 6 sq. in. of anti-pull-through material holding the battery in place and will calculate to a load of just over 8 lbs/sq. in. with a 50 lb. battery, less than half the loading on the floor of the roll bar plates. Make a metal hold-down strap from a piece of 1/8" thick x 3/4" or 1" wide steel strap material. There's no spec on this piece, but you want it to be stout. Like the rule says, no strapping tape or other cheezy material like plumber's tape. Drill a 3/8" hole in each end of the strap and use 2 lock nuts and flat washers on the studs to snug the battery down and you're bulletproof.

As far as the battery box goes, you're free to make your own (sealed) box as outlined in the rule. Those cheezy plastic marine boxes won't make it here. Use rubber grommets in the side or end of the box to run your cables through and remember to run the cables through the grommets and slide your heat shrink tubing on the cable before you install your cable ends . What I'd do is run the cables through the side or end of the box and bend up a nice, bolt-down, removeable top for the box so I could check the water level in the battery. A seal to go between the lid and box can be cut from an old tire innertube. Drill a small hole in the box that'll fit your vent tube. There is only one commercially available plastic box that's NHRA certified, made by Moroso. Summit part # MOR-74050 for $96.95. Taylor makes a real nice aluminum box that's certified under Summit # TAY-48100 for $83.39. Seal the box to the floor and secure it with bolts or sheet metal screws and you're golden. Just a couple of additional side-notes here. Gel-cell or other semi-liquid or dry-cell batteries are NOT excluded from this rule. If you're going to relocate the battery, no matter what type of battery it is, you're going to have to meet the rule with a rear firewall or box. The other thing is, a pickup truck with the battery relocated to the bed does not require a box, only the 3/8" studs/bolts and a metal retainer strap. The rear of the cab serves as a rear firewall to keep acid off the driver.

continued.....