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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 12-09-2003, 01:10 PM
Rex Tener Rex Tener is offline
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Optima 75/35 Red Top Installation

I installed an Optima 75/35 Red Top in my 2001 M Coupe to replace the factory battery which had lost most of its reserve capacity.

I chose the Optima 75/35 over the 34R model due to its slightly smaller physical size, which before has been the impediment with Optima battery installation in the M Coupe. This battery has 10% more CCA that the factory battery and is available at Pep Boys, Costco, and other battery dealers for a very reasonable price.

One additional item needs to be purchased besides the battery. The position of the terminals on the Optima 75/35 do not allow the factory negative ground cable to reach the negative battery post. A negative ground cable that is 13" to 15" in length and is of least 3 gauge is required. I was able to purchase a very well made negative ground battery cable, 15" long, and 2 gauge from Kragen Auto Parts for less than five dollars.

After removing the factory battery, the secondary positive battery cable on the positive battery clamp needs to be moved from its right side attachment to the left side. At this time, it is probably best to remove the factory negative ground cable in preparation for installing the new battery ground cable. Install the battery and attach the positive battery cable. Install the new negative ground cable and attach it to the battery.

The Optima is two inches shorter in length than the factory battery. To prevent the battery from moving around in the battery well, I cut four pieces of 1/2" thick high density foam and placed the at the ends of the battery to secure it. Reinstall all the covers and the install is done.

The top cover fit is not as perfect as I would like. The front left of the cover is not flush with the top of battery well due to the Optima being about a 1/8" to 1/4" taller than the factory battery. However, it does not interfere with the hatch floor covers, so it is something that I am willing to live with. I will probably change two things with my particular installation in the next few days. I will find a shorter ground cable, so that the length is perfect, and use one that has metric hardware. I will buy a piece of 2" thick high density foam to take up the extra space in the battery well instead of using individual pieces of 1/2".

Installation pictures can be found at:

http://www.ninemisfit.com/vehicles/2...ima/index.html

Rex
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Last edited by Rex Tener; 12-09-2003 at 02:15 PM.
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  #2  
Old 12-09-2003, 04:30 PM
Dean Dean is offline
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Looks like a good install, despite the size disparity with the Optima batteries. The Z3 roadster folks also have problems with the positive cable being too short. Unlike the M Coupe, the Z3 battery has traditional screwed in battery hold-downs, which need to be modified for the Optima to fit.

The M Coupe battery has no bolted-down brackets. The battery is secured by a tightly contoured foam pad toward the front of the battery. The stock battery and the Interstate MTP-91 width (side-to-side) dimensions fit the battery box perfectly, so no foam pad bumpers are needed on the side.

Here are some pics of the stock battery and Interstate MTP-91 fit:





For those who jostle your M Coupes around the road or track, keep in mind that the smaller Optima battery is being secured by foam "bumper pads" and a ill-fitting top. It's a floating fit, if you will. You may be comfortable with a unsecured 34lb battery cushioned by foam, but I'm not.

Until someone produces a better fitting sealed battery or a good Optima adapter hardware, I'll stick with the perfect fit of the Interstate MTP-91.

Dean

BTW, the CCA ratings for each battery are:
stock BMW - 650 CCA
Interstate - 700 CCA
Optima 75/35 - 720 CCA
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  #3  
Old 12-09-2003, 04:48 PM
Rex Tener Rex Tener is offline
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Quote:
Originally Posted by Dean
For those who jostle your M Coupes around the road or track, keep in mind that the smaller Optima battery is being secured by foam "bumper pads" and a ill-fitting top. It's a floating fit, if you will. You may be comfortable with a unsecured 34lb battery cushioned by foam, but I'm not.
Actually, I was very surprised when I unhooked the stock battery's terminals to discover that the stock battery free floats around the battery compartment. The only thing holding it still are the battery cables and a piece of BMW foam. Not a great design by BMW.

However, with my added high density pads, the Optima battery is now secured and does not free float with or without the cables attached.

Rex
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  #4  
Old 12-10-2003, 03:38 AM
Anders Anders is offline
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Has the "free-floating" design of the stock battery been attributed to causing any noises? Admittedly, it would take fair thrashing, but would a spirited drive or poor roads generate noises from that area?
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  #5  
Old 12-10-2003, 08:22 AM
Rex Tener Rex Tener is offline
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Quote:
Originally Posted by Anders
Has the "free-floating" design of the stock battery been attributed to causing any noises? Admittedly, it would take fair thrashing, but would a spirited drive or poor roads generate noises from that area?
I have personally never heard any with the stock battery. The stock battery is a close fit in the battery well and considering how stiff the battery cables are, I am not surprised it doesn't move around.

I am/was surprised over how BMW mounted the stock battery. The national sanctioning body that I have raced with over the last fourteen years requires cars to have batteries secured even if they are in enclosed containers and can not be held in place just by battery cables.

Rex
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  #6  
Old 12-10-2003, 08:34 AM
Rex Tener Rex Tener is offline
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Quote:
Originally Posted by Rex Tener
I installed an Optima 75/35 Red Top in my 2001 M Coupe to replace the factory battery which had lost most of its reserve capacity.

Rex
I will say that I know Dean and I have been giving each other a little bit of hard time. I also know my current installation is cosmetically challenged, as I hope to find some professional high density foam or other appropriate material cut professionally to use a spacer for the sides and one end. I originally posted about, and I am still looking for a ground cable from another BMW model of the appropriate length to clean up that part of the installation.

I guess I was a little naive thinking that another option for a battery for our cars was a good thing. Many others have come up with some pretty interesting installs that allow M Coupe owners other options in cosmetic looks and performance. While I will probably not do 90% of them, I think having so many options to pick and choose from in maintaining and customizing our cars makes the M Coupe community a better place.

Rex
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  #7  
Old 12-10-2003, 12:54 PM
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WileECoyote WileECoyote is offline
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To be honest, I don't think foam is the right way to go. I'd look at piecing together an enhanced metal bracket. I can't help but think of battery acid on the foam, myself.

I got myself a Sears Die Hard International - it was a direct fit...
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  #8  
Old 12-10-2003, 01:27 PM
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scottn2retro scottn2retro is offline
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Quote:
Originally Posted by Rex Tener
I am/was surprised over how BMW mounted the stock battery. The national sanctioning body that I have raced with over the last fourteen years requires cars to have batteries secured even if they are in enclosed containers and can not be held in place just by battery cables.
Rex
It may be possible that some M Coupe racers out there have done something similar (gone to smaller batteries) to save weight and may have made some type of hold down brakets.

Is DannO going to use a small, lightweight battery?

btw, do you know the weight of the Optima?
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  #9  
Old 12-10-2003, 01:39 PM
Rex Tener Rex Tener is offline
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Quote:
Originally Posted by WileECoyote
To be honest, I don't think foam is the right way to go. I'd look at piecing together an enhanced metal bracket. I can't help but think of battery acid on the foam, myself.

I got myself a Sears Die Hard International - it was a direct fit...
Yes, I thought the same thing, but BMW seems to be fine with using the expanding foam blocks with the stock battery. I am looking at different materials to see what can be used.

The Optima is a sealed lead acid (SLA) type battery so there is no real danger of acid spill unless it is severely over charged and the internal vents open. It can even be mounted on its side or upside down. I have one mounted on its side in my truck.

The stock battery, Interstate MTP-91, and others are flooded lead acid batteries and need to be kept upright to prevent the potential of acid leaking out. Like a SLA, it will vent fluid if it is over charged also.

Rex
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  #10  
Old 12-10-2003, 01:50 PM
Rex Tener Rex Tener is offline
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Quote:
Originally Posted by scottn2retro
It may be possible that some M Coupe racers out there have done something similar (gone to smaller batteries) to save weight and may have made some type of hold down brakets.
Yes, I am assuming that people are using a more postive mount, especially if their sanctioning body requires it.

Quote:
Originally Posted by scottn2retro
btw, do you know the weight of the Optima?
Optima lists the 75/35 at 33.1 pounds. I have not verified that weight independently.

Rex
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  #11  
Old 12-11-2003, 08:17 AM
Rex Tener Rex Tener is offline
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Optima width

In my search for material to use as a spacer to take up the 2" shorter length of the Optima, I rediscovered the width of the Optima is almost identical to the factory battery.

From the picture I posted above it looks like there is a 1/2" to 3/4" gap on each side of the Optima battery when it is installed. However, the Optima is wider at its base than at its top. Based on my measurments there is less than a 1/10" of difference between their widths at the base. I have included a picture of the base of the Optima to illustrate.

Rex
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  #12  
Old 12-11-2003, 08:19 AM
Rex Tener Rex Tener is offline
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Quote:
Originally Posted by Rex Tener
I have included a picture of the base of the Optima to illustrate.
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  #13  
Old 12-15-2003, 07:07 AM
Rex Tener Rex Tener is offline
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Optima 75/35 Red Top Installation version 1.1

I have revised my Optima installation. I have solved the width, length, and cosmetic issues along with eliminating the step of moving of the secondary positive battery cable. I have not found a solution for the battery well cover poor fitment.

I have been unable to find a supplier for the high density polyethylene foam I used. I got mine from Dell, it was used to suspend a workstation in a box for shipment to me.

I am still looking for a 12-1/2" to 13" negative battery ground cable from another BMW model. Any help with that search would be greatly appreciated.

Revised installation instructions:

http://www.ninemisfit.com/vehicles/2...ima/index.html

Rex
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  #14  
Old 01-09-2004, 06:36 AM
///MDex ///MDex is offline
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Ive been researching OEM battery replacement options for my 00 MC. Ive read the stories about Coupers getting nothing but a click one day as their OEM battery gave out; no warning; nada. Im getting a little anxious about my 00 MC OEM battery, so Id rather replace it sooner than later.

My questions is, is there a tool that one can buy to measure the output of the battery? Now, I know what a voltimeter is, and use one every now an again for my job, so would it be as simple at touching those probes to the neg & pos posts to measure the output?

I know I could probably take the MC to any local A/P store, and theyd check it for free, but Id rather invest in a tool if it can be had for a reasonable cost.
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Old 01-09-2004, 10:06 AM
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Pinecone Pinecone is offline
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The problem is to properly check the battery, you need to check it under a load. You can check the voltage while someone else is cranking the engine for start. Or buy one of the laod testers, like the battery places have.

They have a BIG (for heat) variable resistor along with ampmeer and volt meter. You turn the knob to load the battery and check the voltage under a fairly high amp discharge level.

Of course, if you check the battery voltage not under load and it is low, you have a problem. But a battery can be failing and have a open circuit votlage about right, but be very weak under load.
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  #16  
Old 01-15-2008, 02:24 PM
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Quote:
Originally Posted by Dean View Post
The Z3 roadster folks also have problems with the positive cable being too short. Unlike the M Coupe, the Z3 battery has traditional screwed in battery hold-downs, which need to be modified for the Optima to fit.
Sorry to revive this bad boy but..

I am looking at placing an Optima in a 96 Z3 roadster. I, however, would like to get a yellow top. What modifications or issues do you guys foresee?

Thanks.
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  #17  
Old 01-15-2008, 03:24 PM
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Originally Posted by Smalls! View Post
Sorry to revive this bad boy but..

I am looking at placing an Optima in a 96 Z3 roadster. I, however, would like to get a yellow top. What modifications or issues do you guys foresee?

Thanks.
Why not use the BMW AGM battery?
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  #18  
Old 01-15-2008, 04:22 PM
Smalls! Smalls! is offline
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The car is only driven seasonally, so it dies and needs replacing. The yellow top will hold charge longer, and if it goes out all the way, it can be recharged without harm.
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Old 01-15-2008, 04:23 PM
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Ron Stygar Ron Stygar is offline
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Originally Posted by Smalls! View Post
The car is only driven seasonally, so it dies and needs replacing. The yellow top will hold charge longer, and if it goes out all the way, it can be recharged without harm.
AGM does the same.
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Old 01-15-2008, 04:24 PM
Smalls! Smalls! is offline
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AGM does the same.

Ah I see! What does AGM stand for?
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  #21  
Old 01-15-2008, 04:27 PM
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Ah I see! What does AGM stand for?
Absorbent Glass Mat

Post#6

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  #22  
Old 01-15-2008, 04:34 PM
Smalls! Smalls! is offline
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Excellent information, thank you! Are there any remaining benefits of using a spiral cell battery such as the Optima?
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  #23  
Old 01-15-2008, 04:53 PM
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Ron Stygar Ron Stygar is offline
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Are there any remaining benefits of using a spiral cell battery such as the Optima?
Not familar with Optima. I thought that they were AGM.
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  #24  
Old 01-15-2008, 05:15 PM
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Originally Posted by Ron Stygar View Post
Not familar with Optima. I thought that they were AGM.
You are correct.

http://www.dcbattery.com/optimacatalog.pdf


Sorry for my lack of research, and thank you!
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  #25  
Old 01-15-2008, 07:48 PM
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Note: it's not true that Optimas can be recharged after going completely dead. Nor other AGMs. Don't overbelieve the 'deep-cycle' notion. I'm now sitting on my _second_ dead Optima yellow, this one dead right off the shelf of the store with a date code of June 2007. All of my chargers say it's sulphated, and the desulphation cycle isn't reviving it. Basically, if it goes below about 80% charge for a couple of months, buh-bye. Same thing happened with my last one though it sat for longer.

The only right solution storage of a regular lead acid or an AGM battery is a maintenance charger, even if there's no load on it at all.
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