Electrical Help Please

Battery is dated 1/2020 so it looks like it's 4 years old.

At this point I'm thinking about buying an alternator and a battery both. The alternator is questionable and the battery will take a charge but it sure discharges quickly with the slightest usage. Thoughts?

Where does the voltage regulator come in? Could this be the issue with the alternator giving conflicting readings? (one store says bad the other store says good?) The Parts Store guys weren't sure..........