why does my battery come on but alt is charging battery on 2002 Ford Windstar

lights flicker when u use in buttons like the locks or windows does this van have a voltage regulator

Asked by for the 2002 Ford Windstar
Alternator may be charging battery but, it also may be charging at a lower level because it is worn out and about to go bad. It no longer is producing enough power. Need to have it tested for proper power generation.