Nissan Repair Questions? Ask a Mechanic for Answers ASAP
If the battery is going dead overnite or over the period of a few days or more than it's most likely a drain on the battery and not a fault with the battery itself and/or even the alternator. To begin with, is there anything on the vehicle at all that remains on that you can tell when the ignition is off or is there anything electrical that doesn't work at all when the ignition switch is on?
If you cannot tell, then you are better off testing for a drain. Do you have an ammeter?