Custom Fiberglass storage tub
 

After I pulled the donut spare, rear air bags, compresser, tanks and lines and installed springs, I was pretty much left with this
http://i141.photobucket.com/albums/r...ps7fb6272d.jpg
I pulled the tub that housed the battery and pop riveted a plate in place.
http://i141.photobucket.com/albums/r...ps157b99c4.jpg
http://i141.photobucket.com/albums/r...ps71e54efd.jpg
I built up the walls form walls with cardboard and heat ducting tape which works well for laying fiberglass against btw.
http://i141.photobucket.com/albums/r...ps563b327f.jpg
http://i141.photobucket.com/albums/r...ps1d189059.jpg
http://i141.photobucket.com/albums/r...ps7e9b680a.jpg
http://i141.photobucket.com/albums/r...psecbe3e61.jpg
I also made a small battery box out of cardboard as well and fiberglassed it as well. Once the fiberglass had set up, I ripped the cardboard out and eurothane calked it into the tub. After it had set, I had it sprayed with truck bed liner spray
http://i141.photobucket.com/albums/r...ps0f98cf45.jpg
http://i141.photobucket.com/albums/r...ps04c3dbed.jpg
http://i141.photobucket.com/albums/r...ps0e92c5af.jpg
This is the finished product. Now with the added room under the cargo floor, I can build my custom exhaust. Stay tuned.

i know that size doesn't matter (some of my girls keep telling me that!!! lol), but for some reason, my battery is a bit longer... well, i'd say, by the look of the first picture, about 1-2 inches bigger...

are 4.6iS/4.8iS batteries different from other versions?

looks like you could install (2) 12" subs for the rockin sound system, or you could make the ultimate travel picnic basket spread complete with a full bar and preserved meats.

Nope my 4.4 has the bigger battery to Bosch if i remember correctly. I think he had voltage problems.

The battery I went with is an Odessey battery. It's worked fine since I cut out all of the battery draining parasites like the slowly leaking air ride and then the alarm system would go off when the compressor would kick in, my Dice stereo was sucking power also so I pulled it out as well. My nav unit sh!t the bed so my head unit is down and of course my amp is useless without the nav unit so I'm upgrading the stereo too when I get a chance. I already wrapped the factory plastic sub box in fiberglass and added add MDF to the face to be able to accommodate a 10" kicker sub.

Damn nice storage space. Too bad I love my air ride.

No spare????

Fill it with ice, beer, and meat... tailgate beast!

I do also think you need a better form of battery tie down. What I would do is cut a plate of 1/8" steel to go under the current location of the battery, and weld it to the floor of the car under the fiberglass. The get a crossbar type batter tiedown. That will come with two long bolts, whch could be secured to the plate.Another alternative is to get a dedicated battery box, and bolt that to the floor underneath the fiberglass.

The main concern of a good battery tie down is in the event of an accident. You certainly don't want a heavy object flying around, or leaking acid (not with an AGM). But even though this is in a seperate compartment from the interior, in an accident like a rollover, that battery could end up hitting you in the head the way it is secured now. That slide out tray is hardly adequate protection. The other issue, is that a battery that can move can end up arcing on something, and igniting a fire in an accident.

Over the years, I've run tech inspections for many years at BMW CCA and SCCA driving events. That set up would fail.

do you have a pic or the exhaust?...are you getting the exhaust set up from the X5 where its a sticking out in the middle on the bumper?..