Following the Rules
If you aren't planning to race in any events organized by sanctioning bodies like the NHRA or SCCA then it really doesn't matter how you put your battery in the trunk. However we advise that you attempt to follow the NHRA's rules because they are based on what is safe, and putting a 12V power supply next to a tank full of fuel does warrant some precautions.

The NHRA does not allow for batteries to be mounted inside the driver compartment. A battery can be mounted in the trunk space by either sealing off the trunk space with a rear firewall or sealing the battery in a box. The firewall must be 0.024" thick steel or 0.032" thick aluminum, and must seal off all openings between the trunk and passenger

Avoid this type of box, as they do not meet NHRA or FIA requirements.

compartment. This means you must seal the package tray area on most cars. Most individuals find it easier to simply seal the battery in a box. The box must also also be made from the steel or aluminum thickness specified earlier, or one can use an approved composite battery box. As of this writing the only composite box we know of that is approved by the NHRA (who uses the FIA's approvals) is Moroso's blue battery box. Do not use one of these black marine boxes if you plan to take the car racing as it will not pass inspection. Whichever route you choose, the battery must be secured with a hold-down bracket and 3/8" thick (minimum) bolts through the floor. You cannot just put the battery loose in the box.

In addition to the battery sealing rules you must utilize a cutoff switch visible from the rear of the vehicle. The switch has to cut power to the engine and fuel pump when turned to the 'off' position. This means your alternator and fuel pump must be powered through the cut off switch so that the engine cannot keep running under alternator power. On fuel injected vehicles, since the computer controls the fuel pump and spark, the engine shuts off by simply killing the battery. On a carbureted car you'll need to run a wire to the switch, we've shown you how below.

Sanctioning bodies like the NHRA have strict rules for relocating batteries away from the engine compartment. You either must seal the trunk with 0.032" thick aluminum or 0.024" thick steel as shown here. All holes must be sealed, including the package tray area.	Moroso offers all of the materials needed to relocate your battery. Shown is 8 ft of their 2 ga. battery cable, a heavy duty cutoff switch and compression style battery terminals. The 8 ga. green wire is available from any hardware store and will be used to wire the alternator to the cutoff switch. This will ensure the engine doesn't run off alternator power when the switch is turned off.
Moroso's heavy duty battery cutoff switch must be accessible at the rear of the vehicle to emergency track personnel. The switch knob can be removed to allow the body to be mounted behind a panel.	Most guys simply mount the switch behind the taillight panel with the knob accessible on the outside. We couldn't bring ourselves to drill a 1/2" hole in our car so we searched for other options.
We settled on riveting a bracket to the bottom of the rear valence to mount the switch. A relatively noninvasive approach that we can easily remove should we want to return the car to stock in the future. Other cool ideas are to mount the switch in one of the reverse lights.	The next step is to mount the box in the trunk. We suggest as close to the right wheel as possible. This will help counter balance the driver's weight and also place weight over the wheel to increase traction and weight transfer upon acceleration. The Moroso box is pre-drilled with two holes in the base. We transcribed those to the trunk floor and drilled two 3/8" holes. Be sure to avoid drilling into the fuel tank!
It may be necessary to use a shim, such as we did with some 1/4" particle board, to create a level area to support the box and battery.	While our Dyna-Batt sealed lead-acid battery will not give off fumes, conventional lead-acid batteries do. This requires the box to be vented to the atmosphere. Moroso provides the grommet and tube, you need to create the holes. We used an existing drain hole in the trunk.
Use the two supplied hold down studs to secure the box to the trunk floor. The threaded sections at the top will hold the battery down, meeting the NHRA requirement that the battery be secured to the floor and not just to the battery box.	From under the car we secured the hold down studs with large flat washers and the supplied Nylock nuts.
There are a couple of ways to attach battery terminals and ends to the heavy duty 2-gauge cable. One is to use solder style terminals, and the other is to use these Moroso compression terminals. We prefer this method because it allows the terminal to be easily removed in the event you need to shorten the cable or route it through a panel.	You'll need three sections of cable in all. One to connect from the battery negative terminal to a chassis ground - a frame point under the rear of the car is ideal. The second cable routes from battery positive to the switch 'on' pole. The third section of cable is the longest run, from the switch 'off' pole to the starter relay in the engine compartment. The Moroso box is not pre-drilled for the cables to pass through, you need to do that based on your battery terminal location. Only drill holes large enough to pass the bare cable, attaching the terminals afterwards as shown. This will ensure a tightly sealed box.
Route the battery positive and negative cables through the trunk floor. We found existing factory holes that we could use. Be sure to use a rubber grommet as shown.	The negative cable should be grounded solidly to a frame member. We were able to use one of many existing threaded bosses in the frame member at the rear of the vehicle.
The other cable from the battery box will connect the battery positive terminal to the switch 'on' pole.	The long run of cable will connect from the 'off' pole to the constant 12V side of the starter solenoid. We are also running a 8 Ga. wire (green) along side the main power cable as this wire will tie in to our alternator power wire. This way when the switch is turned to 'off' the alternator power is also killed, shutting down the motor.
Securely route the cable under the car and away from any moving components or exhaust pipes. We used split wire loom to protect the wire from cuts and chaffing that could result in a short. Sub-frame connectors make for a nice routing of the cable.	Once in the engine compartment we connect the cable to the constant 12V starter solenoid terminal. The alternator wire connects to
The cable is pulled up into the engine compartment and secured away from the headers or moving parts. The connection is made to the starter relay.	To connect the alternator to the cutoff switch we simply took the two factory alternator "feed" wires that normally connect to the battery side of the starter relay and connected them directly to the green 8 Ga. wire. We taped up the connection to avoid shorts.
This is what the final installation looks like. The hold down bar must be installed to keep the battery securely strapped to the trunk floor.	The Moroso lid seals the battery. This is an NHRA compliant battery-in-the-trunk setup that will pass any track inspection.

The final step is to check your voltage before starting the car. Check the voltage at the battery terminals, then at the switch terminals. Turn the switch to off and verify the voltage drops to zero on the 'on' terminal of the cutoff switch. Once this is verified you should start the car and verify the engine shuts off if you flip the switch.