Got it
My bad, the way to do it is
WinSCP /console /command "option batch on" "option confirm off" "open ftp://username:Ab%%4d(e6@example.com"
I need to encode % as %%.
WinSCP /console /command "option batch on" "option confirm off" "open ftp://username:Ab%%4d(e6@example.com"
I need to encode % as %%.