Does the guage on the cluster show that its charging? Is the battery light on while running? Check voltage at the battery while its running to make sure the alternator is puting out the correct charge. It sounds like you possibly have something thats draining your battery. If the alternator is sending good voltage to the battery, do a parasitic drain test to see if something is drawing amperage while the jeep is shut off.
1996 Jeep Cherokee- Project-- Rusty's 8in long arm, SYE kit, Teraflex driveshaft, Cragar soft 8's 15x10 with 33x12.5 Firestone Destination MT's, Eaton Tru Trac in the front