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Battery Issues 840??

Printed From: BMW Car Club Forum
Category: Cars & Registers
Forum Name: 8-series
Forum Description: Discussion forum for the 8-series
Printed Date: 20 Feb 2020 at 12:32pm
Software Version: Web Wiz Forums 12.03 -

Topic: Battery Issues 840??
Posted By: HolmeValley840
Subject: Battery Issues 840??
Date Posted: 02 Dec 2018 at 4:05pm
Hi All - I have been having issues with starting my '96 840 after is has been sat for a short time...

Its kept in a garage and if it is left for about a week the battery goes jump starts with no issues.

The batteries are not old and good quality.

Any ideas - I am not technically minded, if anyone is local to the Holme Valley and is, and can spare some time I would be grateful, that goes for any help or guidance generally!

Many Thanks


Posted By: Mike Fishwick
Date Posted: 02 Dec 2018 at 7:23pm
Try measuring the discarge current when the car is standing - it may be quite high, as the 8 Series has lots of electrical devices on it. 

Compare this to the official discharge rate - if it is is within spec, perhaps a small battery charger would be worth buying, to keep the batteries on float charge. 

If the discharge rate is higher than the spec, you will have to pull fuses out to locate the main source of drainage current.  Perhaps your car has an after-market stereo system, or a tracker which needs a new battery.

Remember that a rate of only 0.03 amps amounts to a loss of 22 ampere-hours per month - even with a fullly-charged battery this will drain the battery in about 3 months.  If the battery was not well-charged when the car was stored, it will take a shorter period.

A Z3 is not just for Christmas - it's for life!

Posted By: Mike McCourts
Date Posted: 03 Jan 2019 at 1:08pm
Hi Rob/Mike.
My 840 batteries will only go for a month unused. Any more time in storage and I need to use the jump start. This is even on new batteries but I have found that Bosch are the best as my E24 goes 3 months without charging and that has a Bosch ( and a lot fewer electronic wizardry than the E31 of course).

I have used Yuasa batteries from Halfords but these are not a patch on Bosch, but Halfords will replace under the 5 year warranty.

Looking forward to warmer, dryer weather and a few car show meets.

Mike McCourts.

Posted By: Mike Fishwick
Date Posted: 04 Jan 2019 at 9:33am
Have you measured the discharge current?  Diagnosiis is a lot cheaper than temporarily curing the symptoms with new batteries!

If you want to keep throwing money away it's up  to you . . .

A Z3 is not just for Christmas - it's for life!

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