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paulandchez

It was like the battery just disconnected whilst driving

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So recently had to call AA out. Was driving on and off all day with no issues, then went round a roundabout and half way round the engine fault msg appeared with engine warning light, and lost all power.  Cruised to a stop and all sorts of warnings were going on and off.  

Tried restarting and car tried but wouldn’t fire. (Btw...this was the Mrs out in my car). When I got there, battery was down to 11.5V so was struggling to try to start.  I noticed the clock, date and odo had reset to zero.

when AA got there, we jumped it and it’s been fine since. Error codes were all as expected after flat battery, and none returned after clearing.

only other thing is (despite me telling her over and over again!!!) was that she ran the fuel tank down so it indicated 11 miles left. First thing I did was put £20 of diesel in it before even trying to start it. 

 

So, anyone any idea if this could be a loose or bad connection anywhere, or anything else?  I checked main battery leads.

 

thanks

 

E61 2006 520d

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We tested the alternator and it was charging at around 14.4V once we’d jumped it. 

If it’s charging ok, I’d have thought a duff battery would have shown when starting, not after 45 mins driving....but happy to be told otherwise.

car normally does two 40 ish min drives a day, then longer and shorter ones at weekends 

Edited by paulandchez

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These cars can be very picky with batteries. Age and condition of battery, type (lead acid or AGM), amperage, and whether the battery has been registered and/or coded to the car all have a role to play unfortunately. If the battery is elderly it may just be on the way out. Alternator sounds OK though.

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 It sounds to me more like it ran out of fuel going round the roundabout. The battery went flat trying to start a car with no fuel. The range left isn't that precise.

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On 01/11/2018 at 19:57, JasonH said:

 It sounds to me more like it ran out of fuel going round the roundabout. The battery went flat trying to start a car with no fuel. The range left isn't that precise.

This was my suspicion. Can’t figure out why clock reset though, or why I still get the brake light fail fault still (even though all lights are ok)

 

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Have you checked the high level brake light. Also the car will use a backlight for the brake light if one blows.

 

The clock tends to reset if the voltage momentarily dips below 11V.

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10 minutes ago, paulandchez said:

Cheers guys. Will have a look at the light again and the battery test 

 

The battery test is a ten-minute check that'll leave you confident your charging system and battery are fine. 

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I always question the recharge current of batteries in cars. When you think about it when you start your engine the alternators cars can be very powerful and easily put a massive amount of charge into them which i think can be detrimental to the battery.

All the alternator wants to do governed by the voltage regulator is get the system to 14.5v, so if you have 100A alternator it will initially pump that out to the battery minus any going to run the cars systems. 

From what i understand though the BMW system actually limits this, so must control the voltage regulator to allow the system to rise gradually

 

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