DIY - B6/B7 S4 Battery Relocation to Trunk With Lightweight Battery

Purpose:
I pretty much only did this because I needed a new battery and felt like this would be a fun little project but here’s a bit of justification

Basically, the OEM battery weighs about 60lbs which is crazy heavy for a car battery. There are much much lighter batteries on the market that function just as well for our cars. As for the relocation, I can’t really say it offers that much benefit other than clearing space behind the firewall for your Audi S4 toaster install for crispy toast on the go whenever you want it.

You could claim that it’s removing a bit of weight from the front of the car and putting it behind the rear axle so that there’s less understeer, but with a huge honking V8 in the front, I’m sure it’s negligible

Parts List w/ Links and Costs:
Optima Yellowtop D51R or any other lightweight battery of your choice - $147.05
http://www.amazon.com/Optima-Batteries-8073-167-FFP-YellowTop-Purpose/dp/B00E16M1L0/ref=sr_1_1?ie=UTF8&qid=1433728074&sr=8-1&keywords=D51r&pebp=1433729512573&perid=1BVJF1KS47K46DE2366X
20ft of 1/0 cable (change qty to 20) - $35
http://www.knukonceptz.com/mobile-audio/power-wire/kca-kable/sp/kca-kable-10-ultra-fleks-red-cca-power-ground-cable/
One battery terminal for 1/0 cable- $9.99
http://www.knukonceptz.com/search-results/sp/bassik-positive-battery-terminal/
One ring terminal for 1/0 cable - $1.75 or $6.50 depending on which quality of terminal you want
http://www.knukonceptz.com/search-results/sp/gold-plated-10-ring-terminal-red/
orhttp://www.knukonceptz.com/search-results/sp/set-screw-ring-terminals-10-gauge-pair/
The grounding cable from your original battery
Stuff from your local hardware store:
2x 10" long 1/2" bolts
4x washers for those bolts
2x nuts for those bolts
1x small 3/8" bolt with two washers and a nut for the ground connection
1x Piece of steel or aluminum 14"x1"x1/8"

Tools:
Bear with me as I might be missing a few here

  1. A friend, acquaintance, neighbor, spouse, enemy, prostitute, or even a gnome if the need be to help you lift that battery out of the car and stare at you while you do the rest.
  2. Drill with 1/2" and 3/8" drill bits
  3. Razor blade to strip the 1/0 cable
  4. 13mm socket to remove oem ground
  5. 10mm socket, T20, T30, 6mm triple square and any other tools required to remove the driver’s seat and the seatback on the driver’s side as well as the footwell trim
  6. Any tool I forgot to mention but you end up needing (duh, of course you needed it, I mean c’mon)

Steps:
1. Remove the battery cover and rain tray and begin to remove the battery by disconnecting the terminals and that one pesky retaining screw by the bracing on the firewall. Then have someone help you by grabbing one of the battery handles as you grab the other and pull the battery out of the engine bay. OPTIONAL: put it on your buddy’s desk and claim it’s his new paperweight.

2. Use a 13mm socket to remove the nut for the ground and pull the whole grounding cable out. We’re gonna re-use it in the back.

3. Remove that little thing that looks like a catapult from the terminal so all you have left is a clean terminal on the cable.

http://i.imgur.com/HXxiGL1.jpg

4. Take the cover off the ECU box. Just follow the first 3 minutes or so of this JHM video DIY:
https://www.youtube.com/watch?v=kuTNPxHf_9c

5. Now we’re gonna move to the trunk. Take out that trunk liner and put your back seats down. In-between the two back seats, you’ll see this little T20 bolt. Unscrew it and set it somewhere safe. You should take off the little bracket underneath the bolt as well. Then lift your driver’s side seatback up a bit and pull it towards the passenger side of the car. This will remove that seatback. The back of your car should now look like this:
http://i.imgur.com/X7FOCj4.jpg

6. Now it’s time to pull the front seat out. I personally love video DIY’s and this ones way better than one I could ever make so I’ll just link it here:
https://www.youtube.com/watch?v=Ng3S8HKT9xg

7. Here’s where things might get a bit tricky. We’re gonna start removing the plastic footwell trim. The key is to just pull really hard and in the right order. First, you can just pull up the trim in the driver’s door that goes from the B pillar to the hood latch release. you’ve just gotta wedge your fingers in there and pull. Next, you have to remove the B pillar trim. The non-plastic part up top is the toughest but you only need to remove the bottom two tabs. Again, just PULL and it’ll snap out. The plastic piece underneath it can simply be slid upwards and only has one tab nearest to where the driver sits. Finally, you can remove the plastic trim piece that runs along the back door footwell. Now you should be done with pulling trim
Should look something like this except for the cable

http://i.imgur.com/d8q6Nzv.jpg

8. Really quick, just pop off the fuse box cover and undo the three 10mm bolts that hold the footwell trim in place and pull the footwell trim off so you can see a jungle of wires. Stick a screwdriver or something long through the back of the ECU box so you can see it from the footwell and know where you’re going.

9.Time to feed some cable! I started from the trunk and worked my way to the front. First,I fed the cable through the side trim of the trunk and behind the side bolster of the rear seat to reach that trim piece you just pulled up. Tuck the cable behind the trim piece until it reaches the floor. Here, I fed it under the carpet a bit just to avoid a clip on the trim and I snaked it back so I could follow the trim as closely as I could.

http://i.imgur.com/k6fCPAv.jpg

10. Once I got to the lower B-Pillar trim, I cut a bit out of the inside of the trim so I could run the cable up the trim piece a bit and then back down to avoid some component or something.

http://i.imgur.com/v1Y4i2M.jpg

11. Time for the rest. After the B-pillar trim, I snaked the cable down under all the carpetand foam while sorta following a few other wires going in that direction. I fed it under the carpet basically until I got under the hood release and I snaked it up at the back part of that trim until all the cable was hanging out under the steering column.

http://i.imgur.com/8XBZMdt.jpg

12. Using that screwdriver you stuck behind the ECU earlier as a guide, Thread the remainder of the cable out into the engine bay like so

http://i.imgur.com/0zbZyh7.jpg

13. Cut or drill an opening in the side of the ECU box just big enough for the cable to fit in and then put the cable through that slot or hole and close the ECU box

http://i.imgur.com/c0sIZQ9.jpg

14. Strip the ends of the cable and attach the Ring terminal to the side of the cable in the engine bay and the battery terminal on the side of the cable in the trunk. Or visa-versa if you wanted to do all of that work for no apparent reason. Also go ahead and attach the ring terminal to the junction box on the stock positive terminal and wrap it up real well with some high-temp electrical tape.

http://i.imgur.com/QIr0W72.jpg

15. Moving back to the trunk, position the battery in the spare tire well or anywhere else you want it and drill holes to place those long bolts you bought at the hardware store earlier using the 1/2" drill bit. Also go ahead and drill holes in that piece of metal. Drill one more hole into some metal spot that you’ve sanded down a tad. Place the battery down and put the bolts through the holes with nuts and washers. Tighten them down until you’re sure nothing’s gonna move. Also go ahead an put that grounding bolt through where ever you sanded down and attach the OEM grounding cable there with a nut and a washer. Then attach that grounding cable to your battery as well as the your new positive terminal.

http://i.imgur.com/ka08KJH.jpg

16. Put everything back where you found it and you should be all set!

Cool write-up!

Two questions/comments:

  1. Do you really need to remove the front seat?
  2. Do you really need to mess with the ECU area?

I ask because I ran a similar gauge wire to my trunk along a very similar route for an amp. But I did not pull any seats (just the upright part of the rear seats) and I routed it through a slightly more accessible location in the firewall, I will have to snap a pic. I then tucked it under all the trim and everything.

Yeah if you can, a pic would be awesome! I just felt that it was easiest to route the cable that way and the ECU was the only easily accessible way through the firewall I saw. I also tried following the same path that JHM takes when doing their battery relocations like on MDUBZ’s stage 2. I’m confident that there are multiple ways to route it