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The First operation is to mark the location of the hole I will drill into the original battery holder that is spot welded into the body of the car. In-case you were wondering, it was half the distance between the ends of the battery brace. Use a 7-mm or 5/16-inch drill bit.

Second was to drill a hole into the ž-inch pipe holder. Dill size was a 7-mm or 5/16-inch drill bit.

Third was to use the same metric bolt with a washer and mount it into the factory battery hold down holes. For my battery it was the middle hole.

The next item was to cut to length the battery hold down bolts. Assemble the items and then use the magjic marker to determine how much to cut off. Make sure you measure twice & cut once. In case you are worried about the holders from scruffing the underside of your trunk tray, use some tape or Plasti-Kote to cover then ends of the thread. One thing I noticed, was that one side seams to be slightly taller than the other? I used some red electrical tape to identify the rod that will be located next to the positive terminal. This way I will know where the hold downs are located.

This "custom" battery mount is the same way any other battery is installed in a car. The main difference is the use of a ž-inch pipe holder. As you see in the finished photos, I kept the factory battery holder (triangular in shape), mainly so that I don't lose it - it really does not take up that much space.
The following photos shows the finish product of the battery in place with the new holders installed and the other photo is my carpeted trunk tray that I made to hide the stereo's amplifier mounting system. Maybe I will get to do a write up on my stereo system next year.

SUMMARY:
I installed the battery the weekend of August 21 and so far no issues of the battery coming loose or headlights dimming while blasting the stereo. In case you are wondering about the stock battery ventilation tube. It is still mounted in the car, just tucked away. With a sealed battery, there are no fumes generated and no vent tube required. One last piece of information, I would not recommend this type of battery for the high powered stereo crazies of the world. But if you are looking for light weight & lower cost & you autocross, I would recommend this battery for you. If you plan to road race, look into getting the motorsports version, better safe than sorry. Otherwise, contact me with any questions or if you want to check it out. Good luck!

Subject:Stock Battery Replacement
Cost:$65 Battery + $11 Posts
+ $15 misc.

Good:Light weight & low cost.

Bad:Not for high powered stereo
systems. Need to custom
build battery holder.

Car:2000 Z3 2.8 Roadster

Installer:Who else but me =: )

Equipment:Hawker (Enersys) Genesis
(0769-2007 G16EP)
12 Volt/16 Amp Hours Sealed
Lead Acid Battery.

Gross Weight 13.6 pounds.

Costs Involved:
     > Hawker 12 Volt/16 Ah Sealed Lead Acid Battery, G12V16Ah10EP SLA - Genesis (0769-20007 G16EP). $65.00
     > SAE Battery Posts - Brass terminal set for Genesis batteries. $11.00
     > Battery Holder & 8" posts: $7 at any autoparts store.
     > 3/4" Single sided pipe mount, had one laying around in my box of spare nuts and bolts.

Tools required: Adjustable wrench, hacksaw, 5/16" or 7-mm drill bit, electric drill, weight scale, red tape, magic-marker, 1 Shiner Bock beer and 90 minutes of your time.

WEBSITE:http://www.gotbatteries.com/Productpage.asp?ProductNum=37L105S1

WHY DO THIS:
Well after 5 years of ownership, my stock battery has finally decided to die. No amount of water or recharging would bring her back to life. So I was off to look for a new replacement. The main choices were another BMW battery or an Optima or something else? Well that something else was the Hawker battery. Hawker ($64.95) is the same manufacturer for Dyna-Batt ($155 w/posts), but at a lower cost! The only difference is the decals! I knew about Dyna-Batt from my racing buddies; but, never heard about Hawker. After searching some BMW message boards for "battery" information I found the following from Bimmerforms:
http://forums.bimmerforums.com/forum/showthread.php?t=207492&highlight=battery+hawker

The discussion starts from the stock BMW batteries to the Optima batteries and finally the Hawker / Dyna-Batt batteries. This is where I learned that Dyna-Batt and Hawker were one in the same.
The only potential drawback on the Hawker batteries is that this model that I purchased is not covered under motorsports use. The equivalent motorsports version of mine is the Hawker/Odyssey. They are built tougher and the casing is the color red. I figured that my autocrossing and spirited driving was less abusive than actual road-coarse racing. That is why I picked the plane-Jane black Hawker battery. Now let's get down to the down and dirty installation.

Well after ooh'ing and ahh'ing, it was time to get to working on how to mount my new battery. Incase you don't want to start drilling into your car; there are custom mounting brackets out there. Here is one from Bimmerhaus ($70): http://www.bimmerhaus.com/vendors/wiles.html

Here is the one sold by Dyna-Batt ($80):
http://www.performancedistributors.com/batteries.htm

As you can see, I did not go for those units. Cost was the driving factor. So I started dry fitting the battery to see what I could do. After some brainstorming with a Shiner Bock; something came to my mind. I was off to the local car parts store and also to my spare parts bin. This is what I purchased, sorry, but I forgotten how much I paid for the two items. I think it was under $15 total.