man if your belt is slipping it wont be gripping your alt pulley properly,thus resulting in the alt not running at the speed it should, thus resulting in your flat battery, simple!
Its not the gauge that reads incorrectly on the R32, its the standard oil pressure sensor that goes faulty. Its on the block beside the oil filter housing.
After market ones are cheap enough but don't assume its just the sensor, get the actual engine oil pressure checked to make sure its ok first.
Change or tighten the alternator belt then a simple test can be done to see if the alternator is putting out the correct voltage.
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