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      06-25-2014, 12:32 PM   #1
AUTiger13
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Electrical Question

Mods - please move if this is in the wrong section.

Does anyone happen to know what the battery voltage range is for the M3? I got my battery tested and it read between 13.8-13.9. The reason I ask is because my HIDs have been a pain in the ass. They both light up if I hit the unlock button, but when I crank the engine, typically only one side will light up.

The vendor is telling me that my battery is bad and that getting it replaced will fix the problem. Apparently, BMWs idle voltage is suppose to be 14.3 volts. Can a ~0.3 - 0.4 difference in voltage really cause the problem with my HIDs or is that just BS?
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      06-25-2014, 01:20 PM   #2
Beemdog
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I would not shotgun out the battery just yet. Have you tried charging it overnite with a Battery Tender to see if the HID lights react any differently? Headlights on these cars are controlled by the digital CAN bus so are sensitive to things like electrical noise and such. Again, unless you know the battery is old and ready to replace, I would be careful about just taking the vendor's word for it. The charging voltage is controlled by the car's ECU and varies significantly-- not a steady 14.4V like on many cars with continuously charging alternators.
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      06-25-2014, 01:53 PM   #3
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I do not have access to a battery tender or else I would definitely give it a shot.

The reason I believe it is BS is because sometimes both lights come back on, while most the time they don't. If it was a drop in voltage or a voltage related problem, I would be experiencing both lights not coming back on - which I am not.
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