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Battery choice - trunk mounted


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My '73 2002 came to me with the TEP rear shock tower brace and battery mount.  I like what this does for the overall weight distribution and the extra room in the engine compartment.  Currently, a conventional lead-acid battery lives back there and generally does just fine.  I'm thinking of using that battery temporarily on my '72 Tii project car for systems testing, etc., and am looking for input on the replacement battery for the '73.  I've been contemplating an Optima or similar sealed unit for the trunk location.  If you have a trunk mounted battery, I'd appreciate hearing your thoughts!




Edited by XAVMECH
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I've had good luck with the red Optima batteries.

I did switch to a sealed lead acid for awhile and it didn't last any longer than the Optica which is easier to 

remove and intall in my rear mount.

75 2002 (black) 1990 - 1993

73 2002 tii (malaga) 1994 - 2017

74 2002 tii (verona) 2023 - probably forever

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I thought standard batteries in the trunk were not good?  Leaking fumes and liquid could build up in the trunk and then spark?  Oh and all that next to the gas tank?  A few things I found on th internet,,,



Placing a non-sealed lead-acid without a vent tube battery anywhere except under the hood is a fatal mistake. Lead-acid batteries that aren't sealed give off toxic fumes when charging. The alternator in your car ensures the battery is always charging. Game set match.


I know my opinion on this isn't popular, but it's a bad idea to put any battery in the trunk, and it's a _really_ bad idea to put a standard lead-acid battery in an unventilated trunk. It's somewhat well known that the gas tank in the 2002 series is vulnerable. It forms part of the floor of the trunk, and the filler neck is compromised by a weak plastic hood that clamps on to the tank. In a moderate rear ender, it's not unlikely that gas will spray around the trunk. Heck, in most 2002s I've seen, the trunk smells of gas more often than not.

A battery is a great source of ignition. If the car gets hit hard enough to jostle the battery, and one of the wires come loose, a spark will be generated. Spark + gas fumes = boom.

Also, a lead-acid battery generates hydrogen gas, which if allowed to accumulate in the trunk will also cause a small explosion; and a small explosion in a trunk where a can of gas is stored is a bad thing.

My suggestion, put an Optima no-gas battery under the back seat. That will keep a wall of metal between the source of ignition and the source of fuel.


1976 BMW 2002 Fjord Blue Ireland Stage II • Bilstein Sports • Ireland Headers • Weber 38 • 292 Cam • 9.5:1 Pistons • 123Tune Bluetooth 15" BBS

2016 BMW 535i M Sport

1964 Volvo Amazon Wagon

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35 minutes ago, jrhone said:

Lead-acid batteries that aren't sealed

That's the key.  Any sealed battery (the ones that don't have water fill caps) have a catalyst in the vent to reform the liquid and it drains back into the battery.  Look it up.  But the BMW design for batteries mounted in the trunk, the battery is supposed to be the "international" design with a vent tube that goes thru the trunk floor to vent to the outside even though the battery is sealed type.  They cost a bit more and not all places carry them.  Advance Auto does because I had to search to find one for the 325IX.

A radiator shop is a good place to take a leak.


I have no idea what I'm doing but I know I'm really good at it.

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