# battery question



## aka (Apr 15, 2003)

I just spent the last two hours doing battery maintenence on my Toyota Sienna. As I was topping off the battery fluid, I noticed that there was a bunch of oxidation around the positive terminal so I removed the battery, to my chagrin I saw a bunch of oxidation at the bottom of the pan eating the metal surrounding the battery pan.

Okay, enough of the background data. With the battery in the trunk of the e46 m3 has anyone had the unfortunate experience of cleaning up a battery corrossion mess? I don't know about you, but I for one don't like the placement of the battery. There's lots of space under the hood. Why does BMW put the battery in the trunk?

aka


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## Mr. The Edge (Dec 19, 2001)

aka said:


> I don't know about you, but I for one don't like the placement of the battery. There's lots of space under the hood. Why does BMW put the battery in the trunk?
> 
> aka


better weight distribution is the main reason (or so I've heard)


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## Pinecone (Apr 3, 2002)

A couple of things to do. Clean up the battery area very thoroughly, including rinsiin with baking soda in water to neutralize any acid.

The paint with a good two part epoxy for acid resitance.

Then put in a battery mat (sold by many auto suppiers, in person or on line).

WRT the BMW battery, weight distribution is main reason.

But in favor the BMW battery is a manifold design, where the vent for each cll is captured in a manifold and directed outside the trunk via a vent hose. Most batteries installed under the hood do not have such precaustions, so you get the corrosion.


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## aka (Apr 15, 2003)

Pinecone said:


> A couple of things to do. Clean up the battery area very thoroughly, including rinsiin with baking soda in water to neutralize any acid.
> 
> The paint with a good two part epoxy for acid resitance.
> 
> ...


Thanks for the battery clean-up tips. After reading your post, I re-removed the Sienna's battery, cleaned-up, repainted, and installed a battery mat as suggested. Curiously, the charge on the battery is very strong.

I can buy the weight distribution theory. But, I still don't like it. I wish BMW would have moved something else.

aka


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## TGray5 (Jan 22, 2002)

aka said:


> Thanks for the battery clean-up tips. After reading your post, I re-removed the Sienna's battery, cleaned-up, repainted, and installed a battery mat as suggested. Curiously, the charge on the battery is very strong.
> 
> I can buy the weight distribution theory. But, I still don't like it. I wish BMW would have moved something else.
> 
> aka


Battery in the trunk is awesome IMO...Not only for the weight distribution, but also the fact that heat is a big killer of batteries. None of my BMW batteries have ever had any corrosion on them ever.


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## Pinecone (Apr 3, 2002)

StahlGrauM3 said:


> Battery in the trunk is awesome IMO...Not only for the weight distribution, but also the fact that heat is a big killer of batteries. None of my BMW batteries have ever had any corrosion on them ever.


Exactly, on all three counts.

The manifold venting keeps the corrosive gases away from things to corrode.

In the "old" days, moving the battery to the trunk was one of the first handling mods you made.

WRT battery life, BMW batteries seem to last longer than most batteries.

WRT what to move for weight distribution, the best thing to move back is the engine.  But means a lot more changes than the battery.


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## SupraRZ (Apr 16, 2003)

aka said:


> I just spent the last two hours doing battery maintenence on my Toyota Sienna. As I was topping off the battery fluid, I noticed that there was a bunch of oxidation around the positive terminal so I removed the battery, to my chagrin I saw a bunch of oxidation at the bottom of the pan eating the metal surrounding the battery pan.
> 
> Okay, enough of the background data. With the battery in the trunk of the e46 m3 has anyone had the unfortunate experience of cleaning up a battery corrossion mess? I don't know about you, but I for one don't like the placement of the battery. There's lots of space under the hood. Why does BMW put the battery in the trunk?
> 
> aka


Worst comes to worst, a new battery from Costco will only cost you $35.

Edit: You can also cover the terminals w/ lithium grease, which will significantly reduce oxidation.


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## aka (Apr 15, 2003)

*thanks for the tip*



SupraRZ said:


> Worst comes to worst, a new battery from Costco will only cost you $35.
> 
> Edit: You can also cover the terminals w/ lithium grease, which will significantly reduce oxidation.


Go idea. I'll give the grease a go.


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## jw (Dec 21, 2001)

___lk___ said:


> and much safer jump starts, fwiw.


Battery will last longer in the trunk than in the engine, too.


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## jw (Dec 21, 2001)

DougDogs said:


> Yes, batteries in the engine never last long!
> 
> (sorry, couldn't resist the joke! :angel: )


For the skeptics... 
http://www.uuhome.de/william.darden/carfaq11.htm

11.3. Chrysler studies have shown that relocating the battery outside the engine compartment has increased the average battery life by eight months. Relocating the starting battery to the trunk or passenger compartment, as Mazda did in their Miata a number of years ago, is becoming more popular by the car manufacturers. This battery placement is being used by a number of car manufacturers to protect the batteries from the high under hood temperatures. However, sealed AGM or gel cell type batteries must be used because they produce little or no gas. If a gel cell is used as a starting battery, the charging system voltages are very critical, may need to be lowered to keep from overcharging the battery.


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