My parent's 2018 Mazda 6 with roughly 95,000km (59,030 miles) has recently tripped some sort of warning on the display of the car saying "Battery management system malfunction" alongside the i-stop light blinking with an amber colour. The dealership checked the battery and said it's fine but the alternator is the problem (they didn't provide any details) and of course want to replace the alternator. Will a bad alternator trip that warning or is it something else considering I don't trust the dealer at all and is there any way to prolong the life of the car before a new alternator can be put in? I tried looking for a rebuilt one at local parts stores but there are none available for that make of the car.

Thanks