For those who are curious.. the stock 135i battery weighs 55-56 lb

[crzy4135i]

For comparison


It fits and the car runs (in the driveway) but I did not have time to drive it around to be sure it has enough capacity to prevent getting stranded somewhere. If it works I'll need to fabricate something to secure the battery.



I removed this battery before selling my last car so if it doesn't work I'm not out too much.:biggrin:

[frimmelnojerz]

see i thought about the whole lightweight battery thing but in car where the battery is being placed over(give or take) the back axel and adding to the overall balance of the car i don't see much point in reducing the size of said battery. but...cool.

[crzy4135i]

Originally Posted by Frimmelnojerz

see i thought about the whole lightweight battery thing but in car where the battery is being placed over(give or take) the back axel and adding to the overall balance of the car i don't see much point in reducing the size of said battery. but...cool.

I guess it depends on what each person wants to do. You could save 30lb by switching batteries, then add the extra weight of a mobility kit to support running non-runflat michelin PS2 tires that weigh 4lb/tire less than stock runflats. Of course, if I was really concerned about overall weight I would get serious about my diet.

[stylinexpat]

Thanks for the post and details:thumbup:

[F0Bman]

Damn thats a lot of weight but is like totally needed for all the cranking power the BMW needs.

[crzy4135i]

Originally Posted by F0Bman

Damn thats a lot of weight but is like totally needed for all the cranking power the BMW needs.

Actually, the engine cranked fine with the smaller battery. I turned the car off and started it a few times to test. I'm more concerned with anything that runs while the car is off. It might drain the smaller battery too much. For example, does the electric water pump run after the car is shut down? Does the comfort access feature draw power with the car off?

[Impulse]

The water pump does for sure. The comfort access does but its a pretty small draw compared to the water pump.

[mikeo]

Great information, crzy4135i, thanks for posting.

[crzy4135i]

Originally Posted by mikeo

Great information, crzy4135i, thanks for posting.

Thanks. I'm not sure it will work out but figured I would share what I have so far.

Now someone needs to remove the rear bumper and locate the infamous balast weight.:wink:

[dma550]

or, you can go with the voltphreaks 4lb LI ion phosphate

http://voltphreaks.com/

People are using them in the Lotus elise/exige and track Beemers, but I don't think they would work well as a daily.

[twenzel]

I ran the PC545 (12 lbs) Odyssey battery in my 350Z for a while. It saved about 40 lbs. The problem is that it only lasted for about a year. Its good for a track car but not recommended for daily driving, unless you carry a set of jump cables with you all the time.

[crzy4135i]

Originally Posted by dma550

or, you can go with the voltphreaks 4lb LI ion phosphate

http://voltphreaks.com/

People are using them in the Lotus elise/exige and track Beemers, but I don't think they would work well as a daily.

I used the PC925 in my '00 S4 for quite awhile with no problems. I don't recall exact but it was over a year. Of course, I never listened to the radio while the engine was off due to worrying about it running low.

[BerkTechnology]

Great info! Thanks for taking the time to share.

Lots of the E90/92 guys have already started using the lightweight batteries. Most of the sub ~20lbs batteries only last about a year. The current demands on these Bimmers is too much for them. Regardless of the car, I seem to go through the lightweight batteries about once a year.

But I'm going to replace that battery anyways..... :biggrin:

[aus]

So is there "Efficient Dynamic's" in the 1?

[plosta]

Stock battery in my 128 says 725 cranking amps and 90amp hours while the PC925 has 925 cranking amps and 28 amp hours. The PC925 is supposed to have a service life of 8 to 12 years. As long as your car starts quickly and you are not running everything without the motor running the PC925 will do the job.

[Red135]

I thought the problem with replacing the battery was that it had to be able to handle multiple charging cycles because the system charges during breaking and coasting.

[crzy4135i]

Originally Posted by Red135

I thought the problem with replacing the battery was that it had to be able to handle multiple charging cycles because the system charges during breaking and coasting.

BMW allegedly uses an AGM battery for that reason. They can handle being partially charged and more charge cycles, etc. The
lightweight Odyssey batteries are AGM..

I say "allegedly" because the portly stock battery shown in the picture looks just like a standard old style lead acid battery. It even has the green dot and you can see what looks like acid/water fill ports under the stickers. I'm confused.

IF you read the tech info posted somewhere on this board, the efficient dynamic feature is turned off if the voltage sensor determines the battery isn't keeping up. So.. if I install the smaller Odyssey battery and it can't keep up.. the sensor should defeat the efficient dynamic charging function and allow the alternator to function like all other cars do.

[Red135]

Originally Posted by crzy4135i

The lightweight Odyssey batteries are AGM..

I didn't realize the Odyssey was also AGM. My bad.

I did read the tech info, that is why I asked the question. :wink:

[crzy4135i]

Originally Posted by Red135

I didn't realize the Odyssey was also AGM. My bad.

I did read the tech info, that is why I asked the question. :wink:

No problem and I wasn't trying to be rude. I'm only letting you know the source of my info.

[IDBMW]

Originally Posted by crzy4135i

BMW allegedly uses an AGM battery for that reason. They can handle being partially charged and more charge cycles, etc. The
lightweight Odyssey batteries are AGM..

IF you read the tech info posted somewhere on this board, the efficient dynamic feature is turned off if the voltage sensor determines the battery isn't keeping up. So.. if I install the smaller Odyssey battery and it can't keep up.. the sensor should defeat the efficient dynamic charging function and allow the alternator to function like all other cars do.

Wouldn’t that defeat the purpose of saving weight? If I used a smaller battery that needed to be charged all the time the alternator would be tapping the power from the engine constantly. With the original battery the alternator would only charge on coasting. Which would use more power in the long run? The heaver battery or the additional drag on the alternator all the time.

IMO the lighter battery is not worth it unless you are going to only track the car then you would be tearing it apart to save several hundred pounds and it would make a big difference then. Things like a CF hood, lighter wheels, etc. would be money better spent and you would not have to worry about the car starting.

[crzy4135i]

Originally Posted by IDBMW

Wouldn’t that defeat the purpose of saving weight? If I used a smaller battery that needed to be charged all the time the alternator would be tapping the power from the engine constantly. With the original battery the alternator would only charge on coasting. Which would use more power in the long run? The heaver battery or the additional drag on the alternator all the time.

IMO the lighter battery is not worth it unless you are going to only track the car then you would be tearing it apart to save several hundred pounds and it would make a big difference then. Things like a CF hood, lighter wheels, etc. would be money better spent and you would not have to worry about the car starting.

You make valid points and I will most likely leave the stock battery installed. The main thing for me is I already had this lightweight battery from my last car and I wanted to at least try it in this car. For me, I believe it would be a hassle to swap the stock battery back in for dealer visits. That's one of the drawbacks of having a car under warranty.

How much hp does the alternator use? It depends on the electrical load, and I believe it ranges from 1-6hp. The efficient dynamic function might still run the alternator during acceleration if your driving style doesn't allow it to maintain the stock battery at a minimum level.

Let me go through a few numbers, just for the hell of it.

Assuming the alternator uses 6hp at max electrical load..
Stock car: 3300/320=10.3lb/hp
Using the smaller battery: 3270/314=10.4 lb/hp
In this case, installing the lighter battery would actually hurt the lb/hp ratio!

For the lighter battery to break even, the alternator couldn't use more than 2.52hp (assuming it doesn't use any with the stock battery durning accel)
3270/(320-x)=10.3, x=2.52hp

Thanks for the helpful posts! The CF hood, lighter wheels/tires and other weight saving options do make more sense than the battery.. unless I can install an AMP meter on the alternator output.

[holo777]

I would also pass on doing this mod as a weight savings. To get an Odyssey battery that has even close to the stock capacity (76AH for the Odyssey vs 90AH stock) the Odyssey battery still weighs 58lbs. Any weight savings you get is at the risk on not having the required battery capacity. Now if you can find a Lithium Ion battery out there with a 90AH capacity we might be in business, but several hundred dollars poorer.