Hello everyone,
i have a small doubt about my ESC, it is a 50A Hobbywing ESC 3s-4s.
So can i use this ESC with a fully charged 4s battery(voltage=16.8V).

Thank you,

Yes , it can handle a fully charged 4s

Information is also needed regarding the Load that you are gonna use. Load current should not exceed 50A.  Also check if 50A is burst current or continuous current as specified by manufacturer. If 50A burst current than load should be much less than 50A.