Friday, June 22, 2007

Installed lightweight 4.5 pound battery in BMW M3, replacing stock 50 pounder!

So, we've made a lightweight 4 pound starter battery for gas cars. Took us several prototypes before we got to our final working configuration. Issues like power, charging, casing, configuration, balancing, hookup terminals, etc, had to be figured out. But in the end, it was worth it! We've saved almost 45 pounds from the BMW M3. Notice the lack of a spare tire in the M3, there's run-flat tires and an air compressor instead, to save weight. The stock 3 series has a spare.

This is the battery we are replacing! Notice how much smaller it's going to be.


A size comparison versus the stock M3 battery. The battery in front is from the Scion xA, and was hooked up so that we wouldn't lose our settings from the car.


Installed battery. We needed to use a one foot extension cable because the stock positive clamp on the M3 wasn't flexible enough to reach the positive terminal of the battery.

19 comments:

Anonymous said...

I am willing to bet that you could save another 5 LBS in wire if you were to install the new smaller battery under the hood close to the starter. The original battery wasn't put up front because of size and weight issues, But it doesn't look like you will have any of those.
How many amp hours is the new pack? What is it's maximum current draw?

Tony said...

Hmmm, yes the wires are pretty heavy from front to back, possibly more than 5 LBS. Something to consider. It's 12Ah, maybe 500+ amps max.

stephen said...

You do realize that BMW puts their battery compartment in the trunk for a specific reason right? Other than safety issues, it is for the reason of their 50/50 weight distribution that is known in all their vehicles.

Tony said...

Yes the weight distribution will be changed by moving the battery out of the trunk and into the engine compartment. It's actually SAFER not having the lead-acid battery in the trunk, though! Notice the vent hose on the stock battery, this is required by law since the battery is in the trunk. If the battery is in the engine compartment, you don't need this. But yes I agree that weight distribution would change by moving the battery. Hmmm, maybe you could move something else to offset this?

Dave said...

Tony,

I read your announcement on the e46Fanatics board. I would like to invite you to comment on the M5board at well. Here is the link to a thread I started on weight savings for the e39 M5:

http://www.m5board.com/vbulletin/showthread.php?p=1079407#post1079407

Lightweight batteries commanded a lot of discussion. A 4.5 lb battery is of great interest. Our OEM battery weighs a monstrous 61.5 lbs. If you could comment on: 1) CCA (I live in Chicago); 2) increasing capacity by hooking up two or more in parallel.

Also, upping the warranty coverage from your current 1 year could be a big selling point. My credit card is getting itchy... ;-)

Thanks

Dave

David said...

Well, the charging system is not set up for Lipos... (I'm Assuming these are A123 cells)....

Unless there is a circuit to manage charging, this could be scary... OTOH, if it was fully engineered for automotive applications, it could be great.

Anonymous said...

Dave
Can you explain what is the issue with managing the charging? What would be different about charging these batteries with a regular alternator / charging circuit rather than lead acid?

Anonymous said...

M3 doesn't come with run-flat tires in stock form.

Anonymous said...

While the weight distribution is effected, its ridiculously slight. We're talking a loss of 45 pound on a roughly ~3200 car before passengers. Besides, these cars arent corner balanced from the factory.

Seems like a great product for racers. Wish I'd have known about it just a few weeks before as I just converted my 911 to an odyssey from the original dual conventional batteries. As I had to buy a conversion kit to relocate the cell to the smugglers trunk, the cost differential would have been pretty slight < $100 when it was all done and saved an additional 10-12 pounds. I'm sure a lot of PCA racers will be interested. Cool product!

Anonymous said...

Last night I finished installing the 6.5 lb battery in my 2002 BMW M roadster. Car starts fine, and battery still reads 13.3V after 10 starts. I've shed about 35 lbs. Thanks!

Just a suggestion... change the lugs to just a 5/16" or 3/8" threaded brass or copper rod. The existing lugs put too much restriction on connector orientation and if one uses a fancy ring terminal connector (say a StreetWires PRI4 or PRI0), there's risk of damage if the connector gets knocked.

Vince S said...

Installed on my track car. Works flawlessly.

For BMWs, I highly recommend building custom brackets to hold the battery. Avoid ziptires and duct tapes.

Anonymous said...

Alright, its been nearly 3 months since the last update.

How about some updated news?

Anonymous said...

Whoever anonymous is said it right...

5 months with no updates what-so-ever now.

These guys actually run a company selling lithium batteries (that's how I found this place), but they haven't posted a damn thing since June?

Pathetic!

Tony said...

There's been a holdup on our EV project (not our fault!) so we haven't been able to work on it. We're trying to get around it, though.

Anonymous said...

What stage are you at with your conversion? There are always hold ups when converting a car, that is the nature of doing a conversion. What is your next step?

Compaq notebook battery said...

Wow.! Period then exclamation mark because its quite the revolution! Its about time that companies endure a bit of a twist in their representation, its not often we get to see something like this but hey it'll be worth the production! Whether people think it to be unique or not, Im my own individual and nothing will get in the way of my vision!

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Cialis said...

Wow, that is a huge difference in weight!

Elliott Broidy said...

Wow