My car has a manual transmission.
Thank you for contacting us today in regards to your 2008 Mercedes-Benz not holding a charge. When the alternator and battery have both been replaced at the same time, a common culprit is either an issue with the battery cables or the voltage regulator (which if I'm not mistaken is not a part of the actual alternator on a 2008 Mercedes-Benz CLC 180).
If this is the case, it will typically produce a P2503 OBD-II trouble code when connected to a diagnostic reader.
Electrical gremlins like this are very difficult to pinpoint without being onsite and completing an electrical system diagnostic check-up. The best advice I can offer is to contact one of our local ASE certified mechanics so they can arrive on site to complete the inspection and determine why your battery won't hold a charge.
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