Battery Replacement and Relocation
Everything you need to know about moving that hunk of lead

Brian Collier

The easiest way to improve the performance of your CRX is to "add lightness". Short of gutting the interior (or putting yourself on the Atkins diet), replacing your porker of a stock battery with a svelte Hawker Odyssey is one of the quickest routes to lightening your CRX. While you're at it, you can put the Odyssey in the cabin of your CRX to improve weight distribution and free up room in the engine bay for more important components like a turbo intercooler.

Purpose of This Project

Would you willingly drive around town with 30 pounds of lead strapped to the hood of your car? No? Well, that's basically what your battery is. Granted, you need something to provide the juice when you want to start the car, but wouldn't you rather use something that weighs half as much? If you consider that every six pounds of weight you save is equivalent to one horsepower, you can see where simply loosing some of that battery pork could help the performance of your Honda, whether you're driving on the street or the track. 


Battery Choice

Some people have successfully installed motorcycle batteries into their Hondas. This route has its advantages. A motorcycle battery is cheap, light, and easy to source, but it also vents gas and can leak, just like your stock battery. That's fine if you keep it under the hood or in a sealed box, but for this project, we're going to move the battery into the cabin: not a place where you want noxious gasses and acid that can eat up your interior or your flesh. You could replace your stock battery with an Optima, but the smallest of these suckers weighs 33 pounds and costs a substantial percentage more than your stock unit. If you're going to swap, you might as well get something lighter. 


The Hawker Odyssey looks positively hobbit-like next to the stock battery.

Hawker offers a battery called the Odyssey that weighs half of a stock unit and takes up half the space. They call the construction of the battery "Drycell". It's a starved electrolyte battery, which means the electrolyte is absorbed in the separator material and the battery itself is sealed. No acid to spill and no gases to vent. The battery meets the US Department of Transportation requirements for a non-spillable battery, and UPS will ship it without a hazardous material rating. You can mount the battery in any orientation except inverted -- upright, sideways, diagonally -- you could drive around with this thing in your lap if you want. 

The recommended replacement model for the CRX is the Odyssey PC680. You can purchase these with or without a metal casing, the weight difference is about a pound, and the price difference is $10. The PC680 weighs 15 pounds, measures 7 3/16" X 3 1/16" X 7 3/16", and puts out 210 CCA at 0 degrees F.  It has a 6 to 10 year service life and a 3 year full warranty for automotive use. The best price I found for the Odyssey was at Battery Mart, and their delivery was amazingly quick, so I can recommend them as a source.

If you're a car stereo nut with multiple amps and subs, you would probably be fine with the PC680, but I would recommend using a different Odyssey model with a higher ampere-hour rating. I (stupidly) let the PC680 run my stereo and subwoofer setup for about 2 hours while I was working on some other parts of my CRX and had to jump start it when I was done. The PC680 recovered perfectly and hasn't had any trouble handling things when the car is running or when I don't leave the stereo on for hours at a time. The literature on the battery says it can withstand 400 complete discharges, but I don't want to test that myself. 

Why Move the Battery

When I first received the PC680, I installed it in the stock location to test it out. I wanted to be sure it would start the car reliably before I went through the hassle of running new power cables into the cabin. It is possible to mount the Odyssey in the stock tray with a battery strap and stop there, since you would save a lot work and weight. However, the impetus for my project was more than just weight savings. I have a future turbo setup similar to Scarrie's challenge car that includes an intercooler designed to mount  in the stock battery location, so I had to get the battery out of there. I could have mounted the Odyssey in the hatch area where most people relocate their batteries, but I didn't want anything else in the hatch competing for cargo space. I looked at the PC680 and said, "I have a light battery small enough to fit into the storage bin behind the seats, why not put it there?"

Parts List
The specific items in this parts list can be substituted with other materials to suit your personal application.
- Hawker Odyssey PC 680 battery
- Hawker SAE automotive battery terminals
- SAE terminal connectors
- Monster Cable® 500Watt amplifier installation kit
- Includes:

18 feet of 4 gauge red insulated wire
3 feet of 4 gauge black insulated wire
Fuse holder
60 amp fuse
You can probably put your own cabling kit together with component parts for less money, but I went with this kit after I spent hours driving from Radio Shack to Pep Boys to Circuit City trying to track down all the pieces and still couldn't locate everything included in this one kit.
- Monster Cable® 4 gauge to 8 gauge power distribution block
- Heat shrink tubing   
- Ring terminals
- Rubber coated cable straps
- Cable ties
- Assorted sheet metal screws


Relocation Procedure

Disconnect and remove the stock battery. Follow the ground cable down to the small bracket attached to the body and cut the wire at the bracket, but leave the ground wire running to the transmission housing. Remove the terminal connector on the positive wire so that the wire to the fuse block and the wire to the starter come apart. You can re-wire both of these with fresh cable, but mine were in good shape, so I reused them. Strip about 3/4 of an inch of insulation from the ends of each of these wires and connect them to the output of the power distribution block. Let all this rest in the empty battery tray for now.


Remove the large storage bin by unscrewing the four screws inside and the two attached to the small storage boxes on either side. You might also want to undo the four bolts that hold down the upright divider and pull that out of the way as well. 

It is possible to simply put the battery in the bin and cut holes for the cables, but I wanted to mount the battery to the car, not the plastic of the box. I think the battery might be prone to sliding around if it just sits on the hard plastic, but there is rubber insulating material under the box that helps keep the battery in place and also keeps it from squeaking every time you turn a corner. 

To get the battery to sit on the rubber insulation, you have to cut a hole in the bin. If you have a RotoZip, or some other spiral saw, this will be a breeze, but a Dremel tool or a small coping saw will also work. Lay the battery in the tray and use a marker or pencil to mark around it so you will know where to cut. Be sure to allow for room around the terminals for the cables and connectors. I oriented the battery with the terminals facing forward so that it would be easy to get jumper cables in there if I have to. In doing so, I had to cut slots into the upper part of the storage tray. This didn't bother me, but you might want to experiment with different positions. Once you think you have the bin cut appropriately, put it back in the car and mark around the new hole to show where battery will sit on the insulation. It's important to do this so you can route the cables in the appropriate place while the bin is out of the way.

Cables-s-s in the pockets-s-s. The extra ground wire is for an amp.

Speaking of cables, you can start in the engine bay and work in, or inside the car and work out. I started at the battery and worked toward the engine. Beginning with the negative cable, you need to attach a ring terminal on one end (if you didn't buy a cable with one already attached). Measure out how long your negative lead will be and drill a pilot hole appropriate for the size of your sheet metal screw into the car body somewhere off to the passenger side or near the floorboard. This hole is for your ground point. I put mine under the small passenger side storage box so I could keep the cable short and to be sure I wasn't going to drill into the gas tank or something equally hazardous. 

If I were doing this again, I would put my ground point in the hatch, because the cable was so thick the small storage box wouldn't sit back into its spot. I ended up just cutting a section out of the bottom of that box since I never use it, which makes it easy for me to get to that ground point if I need to without ripping up carpet again. 

Scuff up the metal around the hole you just drilled. You want to get all paint, dirt, chicken feathers and such scraped off so you have clean bare metal all around the hole. Drop a screw though the ring terminal and screw it into the hole. Point the cable at your battery and attach an SAE terminal connector on the other end. Make sure your cable will reach your battery without the terminal connector hitting anything metal, and use heat shrink tubing at both ends of the cable to make your connections look professional. Use a cable strap attached to the car body to hold the cable in place. If you're careful, you can position the strap under the edge of the storage box to keep it from cutting into the cable. Hurray, you've made a ground connection!  


Now comes the fun part: running the positive cable. You can see how I routed mine toward the passenger side in the photo above. First though, figure out where you want to mount your fuse. I attached mine to the upper tray in the storage bin in front of the battery. Cut a short length of cable that will reach comfortably from the positive terminal to the fuse holder. On one end attach an SAE terminal connector, on the other end connect one side of the fuse holder. Attach the other side of the fuse holder to your looooooong piece of positive cable. Be sure you have more than you think you will need to reach through the firewall and into the engine bay where your power distribution block is waiting. Attach your fuse holder to the storage bin with screws.

Start popping off the plastic plugs that hold the carpet and trim down. There is a plug under the small storage box on the passenger side, a big plug on the floor behind the passenger seat, two plugs up front in the passenger foot well kick panel, and two up on the firewall at the top of the carpet. You can remove the passenger seat if you want, but there is plenty of room to work even with the seat in place. If you own a model year CRX with the seatbelts in the door, try to unbolt the seatbelt latch from the door sill so you can pull up the sill trim. It takes a size 40 Torx bit. I broke mine trying to unbolt my latch, so I gave up and fed cable under the carpet the hard way. If you can get the door sill trim all the way off, praise the gods of the sea because you can simply lay the cable alongside the door sill in the convenient plastic holders that Honda built into the car. If you can't get the sill trim up, then you'll have to feed the cable under the carpet from the back and pull it through from the front. You can still get it into the plastic holders, but it's tricky. 


Secret passage to Mordor...I mean...through the firewall.
Once you have the cable up to the passenger foot well, you have to get it through the firewall. You could drill a hole, but there's an easier way. Go outside the car and look into the engine bay. Low in the firewall to the left of the evap canister, where the wheel well meets, you should see a rubber stopper. No wires going through it, just a simple black piece of rubber. 

Pluck it out. Voila, instant passage through the firewall. Need a grommet? No problem. Take that simple rubber stopper and drill a hole in the center of it. Abracadabra, instant grommet.

Pop your new grommet back into the hole, and feed the cable through. It's tricky to reach up behind all the stuff under the dash, but you should be able to work the cable through in an hour or two. 

Just kidding. 

The photo on the right shows approximately where the hole in the firewall comes into the cabin. Obviously it's behind the plastic bits. You will need to reach up behind the insulation material and poke around with your fingers to find the hole and guide the cable through to the engine bay.


Shelob's lair.


The fellowship of the wires.

When you've managed to push and pull your positive cable through firewall, route it to the power distribution block. I attached my block to the front of the shock tower above where the battery used to sit, but you may prefer a different location such as the old battery tray. Trim the cable to an appropriate length, strip some of the insulation off and attach it to the input of your distribution block. Get your trusty drill out and drill holes for more of your sheet metal screws to hold the power block to the car. 

Congratulations, you've completed the positive connection. You're almost finished.


You need something to hold the battery in place. I took a strip of aluminum and bent it into a bracket that fit snugly around the battery, then I drilled holes in the ends and fastened it to the car with sheet metal screws. I did something a little special though. I attached one end of the bracket to the passenger side of the car before I put the storage bin back in. I wanted to be able to get to the other end so I could remove the battery in the future without taking everything apart again, so I put the bin back in the car and attached the free end of the bracket to the car through the storage bin. This meant using a longer screw and drilling an extra hole through the bottom of the bin, but I figure it will save my future self a headache in about 8 years when I replace the battery. Of course, you could bypass all this by simply cutting the entire bottom out of your storage bin. When you attach the bracket, remember that you're over the gas tank, so be careful when you drill.

Before you button everything up, attach both the positive and negative cables, and put the fuse in the fuse holder. You should hear a satisfying click as the electronics in your CRX jump to life. If everything is still dark, double check your connections at each terminal and make certain your ground point touches bare metal. 

Once you've confirmed the juice is flowing, just backtrack and replace everything you removed: carpet, plastic carpet plugs, storage boxes, screws, etc, and take her for a test drive. You should notice an obvious improvement in the front end during slow, sharp cornering, and the change in balance will help your CRX's handling overall.


The Odyssey at home in the Shire.

That's it! Give yourself a beer, or chai, or celebratory drink of choice, and enjoy your CRX.


  Finally, a comprehensive battery relocation article is provided for the CRX owner. Thanks Brian!