The stock battery in our Lotus Elise has completely died. After two winters of storage and not using a battery tender, it would no longer hold a charge. I went to the store to see if I could find a replacement, but all of the size 26 batteries were much heavier. On most cars this would not be a problem, but the additional weight would hurt performance while racing.
The stock battery was only available in Europe and due to SCCA Super Stock rules, I could not go with a super lightweight dry cell battery. The battery I chose was the Odyssey PC925, which was the same weight and orientation as the stock unit. The only problem with the Odyssey battery was that it did not have the standard mounts to be held down with the stock brackets. Sector 111, which engineers Lotus performance parts, carries a part called the Xtender to allow a super lightweight battery to be installed in an Elise. The Xtender also has a cut-off switch, but does not work with the Odyssey PC925 due to being a larger battery. With some simple modifications, the Xtender can be used with the PC925 and below I will document the install.
First, remove the stock battery by using an allen wrench to remove the bracket on the side of the battery.
Behind the battery, you will see another metal bracket mounted on the vertical part of the trunk; that also needs to be removed.
Place the PC925 battery in place and push it into the corner where the stock battery was mounted.
Open up the Xtender parts bags and make sure you have all of the pieces pictured below.
Turn the switch over and hook it up to the stock negative battery cable and the additional supplied cable.
Mount the piece of foam rubber on to the aluminum Xtender as pictured below. I had a difficult time trying to bold the switch on the Xtender, so I took a hack saw and shaved the foam piece in half.
Go to a hardware store and purchase a M8-1.25x60mm metric bolt, a package of fender washers, and a large spacer.
Place the Xtender on top of the battery and ensure the battery is pushed into the corner. You will need to drill a new hole in the aluminum bracket as the available slots will not line up. Before you drill the hole, make sure the battery is in the corner and the Xtender is tight around the battery.
After you drill the hole, you can trim off the extra aluminum that will not longer be needed.
Mount the switch to the Xtender bracket and tighten down the 4 bolts and the battery cables.
Place the stock battery bracket into the original location. Test fit the assembly by taking the new bolt and making sure that the Xtender bracket and hole lines up.
Measure the distance from the bottom of the Xtender to the top of the stock battery bracket. Subtract from the distance the thickness of one of the fender washer. Cut the spacer the required distance and use a sander to make sure it is cut square.
Install the newly cut spacer and place a fender washer between the Xtender and the spacer. Take the bolt with a washer and slip it through the drilled hole and tighten it into place.
Push the battery into the corner, hold the Xtender onto the battery and tighten down the bolt with a 13mm wrench.
Install the battery cables and verify all cable bolts are tight.
Verify the battery is mounted snug and the battery cannot move in any direction.
You have successfully performed a custom install of an Odyssey PC925 in a Lotus Elise. You should buy a battery tender to keep the battery charged during storage. Charging an Odyssey battery with a standard automotive charge will cause permanent damage.
Let me know if you have any questions or help with your install.