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How many volts should your battery be ?

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How many volts should your battery be ?

Postby chubbm » Mon, 05 Feb 2007 15:48:43 UTC

For an 80amp battery on a 530i petrol - the reading was 11.66V (free from halfords)

is this reading a little low for a battery 6m old ?


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Postby agh » Mon, 05 Feb 2007 16:16:04 UTC

Thats really very close to 12 volts.
It is winter, so the voltage may be a little down due to cold.
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Postby mark34bn » Mon, 05 Feb 2007 17:44:19 UTC

When the car is running you should see 13.5 - 14 volts. As above when the engine is switched off.
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Postby sicknotexxx » Mon, 05 Feb 2007 18:50:53 UTC

As long as you around 12v you should be ok its the cranking amps you need to keep an eye on

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Postby blondini » Mon, 05 Feb 2007 19:02:36 UTC

I take it there is a problem that lead to the voltage being checked because 11.66 volts is too low. A fully charged battery with no load should make at least 12.5V. But a poorly battery that has recently had charge can still show a good reading so you need to run the lights for 30 seconds then leave it for say 10 mins before measuring.

With the engine running it shouldn't make much more than 14V when the speed is increased. Then with everything electrical switched on it should still make at least 13V.
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Postby baboo pardesi » Mon, 05 Feb 2007 19:43:12 UTC

Most are 12v..
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Postby Madeira Jon » Tue, 06 Feb 2007 14:18:58 UTC

BLONDINI is quite correct. His suggests a good test. I would suggest 13.5 for a healthy battery. In any case, if the battery is 3 years old or more I would consider changing it. They are cheap anough for security of mind.
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Postby chubbm » Wed, 14 Feb 2007 13:54:27 UTC

Well yet another break down and the car wont start.

called RAC and they told me car has battery drain of 2.5AMP (per day!)

have spent £265 at inde for diagnostics but I guess I will be asking for a refund now !

Going to main dealer next week to get this problem sorted for good

Have taken out fuse 57 from car to see if comms pack was the source of the fault but probably not.

Digital temp. gauge on dashboard now missing the degrees and centrigrade signs

Any ideas anyone ?
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Postby S_a_m » Wed, 14 Feb 2007 14:48:16 UTC

mine reads 13.6 v when under no load, iv got a voltage checker on my amplifier in the boot, when i start playing my music the voltage will drop to around 12v - 12.5 v and i have no idea how old the battery is
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Postby Wicksta » Wed, 14 Feb 2007 15:48:24 UTC

chubbm wrote:Any ideas anyone ?
When I had the same problem they replaced the final stage resistor in my aircon unit, the only symptom I had was the battery going flat all the time.

After they fixed it it was fine for ages but then the battery developed an internal short circuit (maybe because of being run down so much). Since BMW assist replaced that I've not run out of battery once. :)
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