OP: what actually is the problem? A slipping belt causing the alternator not to charge or just a general question on serpentine belt adjustment?

As other have mentioned, the serpentine belt is self adjust by the tensioner. Do you have cold A/C? The compressor is a more heavy load to turn. If compressor, power steering work then I would discount the belt slipping theory and look at the alternator proper.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

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