Chosen Solution
I changed the battery and now it won’t turn on if it’s not connected to the charger. Once it starts I can unplug the charger and the status indicator will change to battery after 10 seconds or so. SMC reset done twice and still no change. Any idea what could be wrong? Thanks.
Double check if all the connections, especially the battery connection (MacBook Air 13” Retina Display Late 2018 Battery Replacement) are seated correctly in their sockets. If all the connections are good and nothing is damaged while repairing your MacBook, you probably have received a bad battery and I would recommend you to contact the store where you ordered it from to have it replaced.