Haven replaced alternator & battery on 1996 Nissan Sentra 1.6 litre. Battery keeps dying, that is, it doesn't seem to be receiving electrical power from the alternator system. I drive for a short distance on battery power alone, then the fuel system shuts down.

you have, or have not replaced anything?

sounds like a bad alternator. if it's been replaced, have it checked with a volt meter to be sure its suppling the correct voltage.