Have the battery load tested and have the alternator tested for proper output.
If you have a multimeter or voltmeter you could do a simple test to see if the alternator is actually working. For that connect the meter across the battery terminals with the engine off. You should see 12.6 volts or so on a fully charged battery. Now start the engine and check again. The voltage should be higher now from 13.6 up to 16 or so volts.
If you mean that the battery goes dead while the car sets overnight, you will need to do a parasitic drain test to determine what is drawing the battery down. That is covered some in
Saturday, January 21st, 2017 AT 3:56 AM