Just had my battery replaced in my 2019 MKC today. Tell tale signs the battery was weak were the following features were turned off by the Battery Management System to conserve battery power (1) welcome lights never activated (2) intelligent access was limited to drivers' door only and (3) auto stop/start feature was disabled without any driver input. My understanding is the auto/start feature at one time continued until the battery died and left owners stranded. Later engineered to automatically disable feature when battery started to get below a certain voltage threshold. The new battery restored all these features, but the auto start/stop feature took about 10 miles of driving before it "learned" a new battery had been installed.
Same thing happened to me. dealer stated battery was good, two weeks later, all troubles started again. Returned to dealer, replaced the battery, and all electrical problems were solved, no more problems. Transmission growl at 22,000 miles later, dealer could not get a replacement, vehicle claimed as a buy-back and I bought a jeep.