<E30> Dual Battery Contemplated

[ingraham@xxxxxxxxxxxxxxxx (Curtis A. Ingraham)]

In BMW Digest v09.n1401 Carl Bassett <Carl.Bassett@domain.elided> wrote:

> Has anybody set up a dual-battery system in their BMW?   Are 
> there any issues/pitfalls/concerns/suggestions to share?
> ...
> Without any aftermarket accessories, what is the normal range of 
> current drain when the car is off?

Less than 100 milliamps.  Expect to see about 40-50 mA.

> I'm new to BMWs and have just acquired a 1987 325iC.  With the 
> battery in the engine bay I am thinking about setting a 2nd 
> battery in the trunk ... I recently have been having problems 
> with not being able to start her after sitting over night.  

Either your battery is about to expire, or you have have a
significant current draw somewhere.  In either case adding
a second battery will add weight and cost but no solution.  

Almost any battery store can load test your battery to 
determine its condition.

E30s are known for several battery drain problems, including
glove box light, trunk light, door lock heater, etc; I'm
sure another reader will fill in the diagnostic details.

> I have an alarm system with shock, motion, and radar sensors 
> that I am sure don't help.  

If you suspect the alarm of drawing too much current, measure
the battery current three ways:

  1. Alarm disarmed.
  2. Alarm armed.
  3. Alarm fuse removed.

Curt Ingraham
72 2002tii
Oakland, California

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