This article serves two purposes. First of all, I am replacing the factory 29+ pound battery in the MR2 with the Odyssey PC680 unit weighing in at a “hefty” 14.8 pounds, effectively creating a 14.2+ pound weight reduction. Additionally, I am relocating the new battery to the front of the car to a location in between the strut towers. Without delving too deep into the weight distribution theory of a mid-engined car, let’s just say that a few tactful weight increases on the front and conversely, weight reductions at the rear greatly improve this car’s handling prowess without upsetting its mid-engine agility.
Required Parts
If you are not keen on relocating the new battery to the front of the car, you can simply remove the factory battery and then install the Odyssey battery in its place. However, for those relocating the battery to the front, in addition to the Odyssey battery you will need the battery mount, roughly 26 ft of 4 gauge battery cable (they should have this at your local parts store for around $1/ft), 4 battery cable ends, a few 10mm nuts and bolts to connect the new ends and to secure the battery mount and finally, a bunch of zip ties.
Procedure
First, disconnect the factory battery by removing the negative (black) cable from the battery. Then remove the battery tie down and lift the battery out of the engine bay. Remove the battery tray by removing the 4 12mm bolts holding it to the car.
Disconnect the negative (black ground) cable from the battery (1) and then disconnect the positive (red) cable (2)
The old battery, tray and tie down removed from the engine bay.
Now take the long length of 4 gauge battery cable and cut it into two equal halves. Strip the ends of each half and place a crimp connector on their ends. Once in place, tug on the connectors to make sure the ends are secure. Next, remove the factory terminals from the existing power and grounding wires that were previously disconnected from the factory battery and then connect the new cables to the existing cables using a 10 mm bolt and nut. Once tightened, go ahead and wrap the connection in electrical tape to insulate it. Then, starting with the other ends of the cables, snake the cable ends along the edge of the engine bay to the underside of the car. Go ahead and secure the cables to hard lines or wire bundles using the zip ties. This will ensure the cables stay in place and do not touch any moving parts in the engine bay.
The new battery cables will bolt directly to the ends of the factory ones so remove the cables ends from these two cables.
Once the new cables are connected to the factory ones, wrap the joints in electrical tape and secure them in place using zip ties. (area circled) The feed the new cables through the engine bay to the underside of the car. (follow the arrows and secure the cables with zip ties as necessary.
Continue snaking the cables along the hard lines underneath the car, securing them with zip ties as necessary until the cables emerge to the front.
Beginning just outside the engine bay, snake the new cables along the hard lines that run underneath the car and secure the cables to them with the zip ties. Take care not to secure the cables on something that will move like a control arm.
Continue to run the battery cables along the hard line path.
Once the battery cables reach the front of the car, you will need to remove the frunk (front trunk) trim, and the spare tire tub. (Note in the following pictures, I have permanently removed the trim and the lid of the tub from my car.) To remove the trim, simply press in the center of the plastic rivets lining its perimeters and pull the trim out. To remove the spare tire tub, first remove the spare tire and then the four 10 mm bolts holding the tub to the car. Pull the tub out and set it aside for modification.
Once the trim is removed, remove the 4 10mm bolts (highlighted) and remove the spare tire tub from the car.
With the tub sat aside, take the Odyssey battery mount and place it on the upper end of the tub. Place the mount where you want the battery to be and using the mount as the template, drill the mounting holes. (If your car is a daily driver, make sure you place the battery mount high enough to allow room for the spare tire and the full size wheel in the event of a flat.) Once the holes are drilled, place the battery in the mount and then secure the battery to the tub using a few 10mm bolts and nuts.
I used the highlighted flat portion on the upper inside of the tub to drill the mounting holes (arrows) for the battery mount. This mounting location is high enough to retain the spare tire.
This is a backside view of the 4 mounting holes with the hardware secured in place.
The Odyssey PC680 battery secured in place.
Before reinstalling the spare tire tub, drill two holes, one on each side of the battery mount, large enough to pass the new battery cables through. Once drilled, thread the battery cables through the holes while reinstalling the tub. Attach the cables to the Odyssey battery, positive side first and then reinstall the trim if desired. Finally, make one more pass under the car and make sure that the rerouted battery cables are secured and do not touch anything that moves. And with that, you are done.
The finished product. (Notice where the battery cables emerge.)
