I read or saw a video somewhere that this can be caused by a faulty diode in the alternator diode pack. Apparently the alternator can still continue charging enough that it would register on a simple test meter but not full blooded charge. The problem is that the faulty diode can drain the battery. Might be OK right now during the good weather but different come winter time.
2015 Antara Exclusiv 2.2 163ps Manual 2WD