New alternator new battery... But.battery still won't hold charge 2008mercury sa

Well not to be blunt but no shit... That's what I explained but why isn't it doing its job and charging.. The alternator is brand new and so is the battery. Ive replaced both but still same prone

I nor anyone else can tell you why the alternator is not charging the battery ‘without’ *hands-on* testing first! Can post some possibilities but the *hands-on* testing will still be required.. Defective (low quality) alternator - wiring circuit to the alt. Test alternator output outage at battery terminals with engine running - should be around 14 volts.