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I have a toyota yaris 2002 mk1 i put a new Battery in. after leaving car off for 15hrs tested it with multimeter it read 11.56v just about cranked engine and started it once started the alternator charges at 13.98 to 14.v so i know alternator is charging could problem lie in alternator diodes or a problem with starter motor or is their a parastic drain some where some times after 12 hrs batt goes to 11.96v 

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Accuracy is important...

Your charging voltage sounds a little bit low, particularly for cold weather. The alternator output (on older cars) is temperature dependent and following a cold start could be as high as 15.5 volts. 14 volts sounds about right for a very hot engine (and very hot alternator) and would be more what you would expect in summer.

If the voltage is falling under 12 volts in 12 hours then that does suggest an unwanted load... so yes, all things considered possibly alternator related but more tests would be needed to be certain.   


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Was the new Battery fully charged? Just because it's a new Battery doesn't mean it's 100% charged.

Also be mindful that stating a car engine from cold in these temperatures we're experiencing will take a lot more power just to turn over the engine due the the 'thicker' Oil and the reduced capacity of the Battery.( A completely different story when the weather is much warmer).

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