The check charging system light comes on even after replacing battery and alternator

This is a case of the charging system being insufficient, even momentarily. This can be caused by a concern with the new alternator (even replacement ones can fail), or the wiring at the alternator. Inspect the connector and the wiring very carefully and check for any damaged terminals or overheating. Also, ensure the belt is not slipping for any reason - either another component driven by the belt that is binding or a concern with a tensioner pulley.