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will changing my auxilliary battery help my car hold its charge for more than 2 days at a time?if not what exactly does it do?car has a new main battery and alternator btw
 

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jonsmiff said:
will changing my auxilliary battery help my car hold its charge for more than 2 days at a time?if not what exactly does it do?car has a new main battery and alternator btw
I didn't know they had an auxilliary battery - where is it?
 

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Discussion Starter #3
its in the boot,inside passenger side rear quarter panel
 

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jonsmiff said:
will changing my auxilliary battery help my car hold its charge for more than 2 days at a time?if not what exactly does it do?car has a new main battery and alternator btw
Mmm-Five
Not all M5 have the aux battery option.
Those vehicles with lots of electrical options or cold climate country tend to have the offering of aux battery.
Its stored in the trunk behind the lh trim panel from memory.
Jonsmiff
If your vehicle is discharging the battery at the rate you describe, then something electrical has gone open circuit & is drawing vast nos of milliamps per hour.
Get a vehicle sparky to look at the alarm & wiring first. Then progress through the other systems looking for the problem.
Good sparkys will have some idea of where to go first & will check earths,
Alternator , starter ,interior / boot lights etc.

One thing is for sure, your aux battery is not going to make any difference.

Good Luck
Farrell
 

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Hi!
If I have understood it right, the aux battery is mainly for the optional car phone and if the car has the petrol heater, it gets power from the aux battery.
The aux battery is not connected to the main system directly so it isn`t any help for startup or adding upp capacity to the main systems.
:typing:
Sakke
 

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Actually, it is connected to the main supply. I have one and when I disconnect the main battery, I still have 12 volts in the system. I must disconnect the auxillary battery as well in order to get the car's electricity system dead. The battery supports the petrol heater and the phone, as DrSakke says.

In my boat, I have a twin battery set-up for the normal use of electricity (lamps, navigation, refrigirator, radio, wind instruments, eco sounding etc)plus one start battery for the engine. If one of the two batteries in the "consumer cirquite" is bad, it will consume whatever the good battery can deliver. The result is very low capacity all the time even if the alternator works its socks off. ;) I have had this experience more than once.
I suggest that you check the capacity of your auxilary battery at a shop where they know what they are doing.

The other option is that your alternator is gone. It may produce just enough electricity when driving but cannot add anything to the "buffer". I know you said you have a new alternator, but if the batteries were very low when you engaged the new alternator, it may have been busted. I have just changed my alternator and I was informed (warned) that bad battries may kill my new alternator. So far, I'm OK.

Good luck! :)
 

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Discussion Starter #8
its a new alt and battery m8,but i see what youre saying about one taking power from another,aux battery is only producing 2 volts when i disconnect it from the car,need a new one,anyone know where to get one of these
 
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