What's that battery in the trunk?

[Tiger]

I am wondering what is that battery in the trunk? Is that for the alarm? I am finding the alarm is acting so bizarre... in the morning, the alarm will not unlock the car. Start it up and back it out into the street to park... then later in the afternoon, the door will unlock for me with the same damn key.

Key battery is new. This saga has been going on since I bought he car... but recently is really something. I also know that lead acid battery don't last that long either... this one is 14 years old.

So I am wondering... is it this small battery in the trunk the real main reason why remote doesn't work when we needed it to be? Where do I buy this battery?

[attack eagle]

huh? what small battery in the trunk?
got pictures?

What alarm?

[Paul in NZ]

any battery place should be able to match it...I took mine(and the related holders and relays out)....no ill effects.Battery was completely dead,previous owner didnt even know it was there,and at one time there had been an acid spill,cos the boot floor was completely covered in baking soda..(under the carpets)

[Tiger]

LOL... you didn't even know... on driver side... behind the cover and just above the wheel well.

I am going to investigate anc change it out. I think this would solve the stupid key problem.

Alarm? Factory installed alarm.

[attack eagle]

yeah because my car doesn't have one... which means it is an add on.

the only battery I am aware of that could be oem fitted would have been the second battery option from the e32

[repenttokyo]

LOL... you didn't even know... on driver side... behind the cover and just above the wheel well.

I am going to investigate anc change it out. I think this would solve the stupid key problem.

Alarm? Factory installed alarm.

my car does not have this battery either.

[Tiger]

Strange... I know mine has it... it is near the factory amp. Small white battery. Paul has an 1989... and mine is 1994... so that means you guys should have it...

Do you have factory alarm system? Or factory keyless entry system?

[attack eagle]

did at one point.

my suggestion? Dump it completely.

Those batteries have a finite life cycle and they turn into a big electrical drain/load after a year or two when they stop holding a charge.

Do you have a factory Cell install? perhaps it is related to that.

I was in there on a loaded 92 535i on labor day and it didn't have it either.

[repenttokyo]

Strange... I know mine has it... it is near the factory amp. Small white battery. Paul has an 1989... and mine is 1994... so that means you guys should have it...

Do you have factory alarm system? Or factory keyless entry system?

no on either count.

[repenttokyo]

did at one point.

my suggestion? Dump it completely.

Those batteries have a finite life cycle and they turn into a big electrical drain/load after a year or two when they stop holding a charge.

Do you have a factory Cell install? perhaps it is related to that.

I was in there on a loaded 92 535i on labor day and it didn't have it either.

I have factory cell, but no battery like this.

[Tiger]

maybe that is the reason why you don't have one.

Eagle... I don't have factory cell phone either... so it is not related to cell. I want to do an experiment with that small battery... replace it and see how the key remote works and if it is consistent solid performance.

[attack eagle]

I took the alarm out myself, so it wasn't 'uninstalled' with the alarm by someone. the battery is unrelated to alarm performance from an electrical standpoint. What it WOULD do is keep you from losing codes for the radio or any other settings, or perhaps keep the alarm from being disabled by simply disconnecting the battery.

[Paul in NZ]

i dont know why /how you come to have the auxilary battery or not.I dont have a phone,but i do have the 10 speaker stereo.As i say my battery was toast,I took it out and have had no issues.I dont see how it would affect alarm /remote performance.If the elcetrical system was that dodgy surely you would be having other issues...I will post my build sheet layer,perhaps we can see what(if any) we have in common to see why the battery is there

[Tiger]

I suspected the alarm uses that as a backup battery... however, I am not sure how the alarm is wired in relation to the battery... does the alarm get the power direct from the aux battery... if so, then if the battery is dead, it would severely limit the voltage to the alarm unit and thereby causing lots of alarm problem... especially the alarm antenae reception problem.

[Tiger]

Another thought is the aux battery is used also for the OBC code lockout... where you can disable the car by punching the code... then this would explain sometime when someone put the code in but later could not get it deactivate.

[GJPinAU]

and probably the little bugger that keeps your doors locked when the main battery fails!

[Paul in NZ]

and probably the little bugger that keeps your doors locked when the main battery fails!

i am no electrical expert bu t from my recollection the aux battery is wired in parrallel to the main battery,but via some sort of relay.Dont think it powered any components seperately but merely added in its little 25 ah only when the main battery dropped below a certain voltage???

[Ross]

Tiger, Tell us more about this battery. To the best of my knowledge it sounds like something(alarm) installed after the car was made. regardless of where it came from the specs ought to be printed on the battery, using that info a replacement should be available.
Aftermarket alarms seem to wreak havok on these cars if improperly done. Even a connection that causes more or less impedance in a given circuit will cause the Bavarian computers to start acting up.

[Tiger]

I will tell you about it once I get back to it... probably tomorrow. It is definitely factory installed battery (not aftermarket). It is located in same location where you would find the factory CD wire harness.

[bubba966]

There certainly was a factory optioned secondary battery in E34's though it's uncommon. It was more common in E32's. Don't recall it being for any specific components, think it was just for extra reserves.

[bubba966]

This battery have a part #? Or does some part of the mount or cabling? Wouldn't mind having an Aux battery in the car. And it's kinda fun to retrofit factory stuff into my car that wasn't optioned on my car.

[Tiger]

I agree it is wired in a special way with two relays or simply one... in event that the battery get disconnected, it would disconnect from main pathway and reserve that battery to only the alarm system... otherwise all the other electrical components in the car will sap it out in no time.

[Paul in NZ]

This battery have a part #? Or does some part of the mount or cabling? Wouldn't mind having an Aux battery in the car. And it's kinda fun to retrofit factory stuff into my car that wasn't optioned on my car.

will try to find some info..i have an idea i have done this before tho....

[Paul in NZ]

http://www.realoem.com/bmw/showparts.do?model=HD12&mospid=47382&btnr=84_0309&hg=84&fg=95

installing kit second battery...although it seems to be a part of a phone system i have not got a phone.
here is my option list.The comments in brackets are my own,sodont take them as the actual meaning...anyone speak german?


200 KATALYSATOR - ENTFALL (no catalytctic converter)

209 LIMITED SLIP DIFFERENTIAL (25%)

226 SPORTS SUSPENSION SETTINGS

291 BMW LM SCHMIEDERAD/KREUZSPEICH (alloy wheels)

302 ALARM SYSTEM

320 MODEL DESIGNATION, DELETION (no model badge)

335 M TECHNIC SPORTPAKET (mtech body kit, front spoiler skirts,rear wing, aero rear bumper cover)

339 SATIN CHROME (matt black finish around windows instead of chrome)

401 SLIDING/VENT ROOF, ELECTRIC

458 SEAT ADJUSTMENT, ELECTRIC. F DRIVER/PASS

481 SPORT SEATS F DRIVER/FRONT PASSENGER

498 HEADRESTS IN REAR, MECHANIC. ADJUSTABLE

500 HEADLIGHT WASHER SYS/INTENSIVE CLEANING

534 AUTOMATIC AIR CONDITIONING

548 SPEEDOMETER WITH KILOMETER READING

560 CO-PILOTS IN RR COMPARTMENT (reading lamps in rear )

563 BEL.MAKE-UP SPIEGEL (make up mirrors(or lights for make up mirror)

571 BOOSTED POWER SUPPLY (140 w alternator)

676 HIFI LOUDSPEAKER SYSTEM

687 RADIO PREPARATION

708 M-SPORT LEATHER STEERING WHEEL II

806 Neuseeland Ausfuehrung

847 erweiterter Kabelbaum

850 ADD FUEL TANK FILLING FOR EXPORT

925 SHIPPING PROTECTION PACKAGE

[Tiger]

Wow... expensive relay.

[Tiger]

Dug in... It is not a battery... I thought it was... I can't find it on Realoem.com...

The part number is 65758366214

[Paul in NZ]

Dug in... It is not a battery... I thought it was... I can't find it on Realoem.com...

The part number is 65758366214

amp???

[bubba966]

www.mileoneparts.com says


Part number 65758366214 was superseded by part number 65756923208.

65756923208 $121.00 Electrical - Alarm system - Sensor - Motion 1991 - 1997

[Tiger]

Ahh... neato... it is kinda big for a motion sensor.