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Old 01-05-2012, 11:29 AM   #1
dcramer
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Join Date: Nov 2010
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e39 battery dead diagnosis help

So ... came back from vacation. car starts up fine, but the battery light is on.

Checked the charging voltage and it is at 13.5, so the alternator is working
It also sometimes turns off the radio, and the heater in an attempt to save the battery.

This morning the battery is dead

Any ideas ?

Dave
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Old 01-05-2012, 11:55 AM   #2
bmwm5lover
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Sounds like what was happening with my jag. Battery sounded weak when starting, lights were flickering randomly and gauges were going nuts. Shortly after needed a battery after being outside in the cold for some hours. All is good now. These cars are super power hungry and if they do not get the consistant supply they need they act up like you wouldn't believe.
Start your car then disconnect the battery. If it dies, you also need an alternator, if it continues running, just a battery.
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Old 01-05-2012, 11:57 AM   #3
dcramer
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The battery is new, as I said the voltage when the car is running is > 13.5 which is well within spec.

These alternators actually have another circuit which turns on the battery light. I have to check that first. Just curious if anyone has any other insight.
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Old 01-05-2012, 01:18 PM   #4
damameke
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Quote:
Originally Posted by dcramer View Post
The battery is new, as I said the voltage when the car is running is > 13.5 which is well within spec.

These alternators actually have another circuit which turns on the battery light. I have to check that first. Just curious if anyone has any other insight.
Had the same issue 2 weeks ago.... car started fine then died.. checked voltage - within range...charged battery for a night.. ran fine the next few days then died again... replaced battery.. all is fine now...

Battery might not be holding charge...
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Old 01-05-2012, 05:02 PM   #5
Dinanstu
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Battery voltage 12.6 Volts - fully charged
12.2 50% charged
11.7 (or less) fully discharged

Alternator is providing the adequate voltage - check belts.
You were on vacation, so I question wether the battery has had enough time to fully recharge. Put it on a charger overnight (u don't have to remove)
Battery connections, clamp them down and check for corrosion. ( I assume you put the battery in?)

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Old 01-05-2012, 05:16 PM   #6
dcramer
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thanks, my money is on the light circuit in the alternator. The battery dying is probably due to lack of charge as you noted.

almost forgot. My rad blew a few days before I left on vacation .... antifreeze all over the alternator...

Last edited by dcramer; 01-05-2012 at 05:19 PM.
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Old 01-06-2012, 09:52 AM   #7
dcramer
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so charged the battery overnight, disconnected from the car. Reconnected it and now the charging voltage is 18.5 V

Now suspecting the alternator

Dave
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