Battery or alternator
 

Hi all newbie here. Wife's 01 Grand Marquis has issues (besides the driver). She works from home so doesn't use the car much. After sitting in driveway for 3 days won't start, just clicks. Never had trouble before. Jump start off my truck. Battery was completely dead, even the radio had lost all programmed stations as if battery was disconnected. No idiot lights showing on dash, but as soon as I undo jumper cables, motor dies. Restart car and check my gauge in truck, I'm showing 10 volts, but rising. After 10 minutes remove cables and stays running for few minutes. Car won't stay running. But still no light on dash. Is this just a bad battery or alternator also? Can't drive to O'Reilly to check, won't stay running long enough, and really don't want to pull alternator if don't need to replace. Bought car 3 yrs ago, no idea how old battery is so will replace anyway.

Your Battery is DEAD -- and needs replacing.
Your battery size is #58. Get the battery with the highest "Cold Cranking Amps" rating.

When connecting/disconnecting the battery, remove the NEGATIVE battery cable FIRST, and connect the NEGATIVE cable LAST.
Your new battery should be of the correct type for your Grand Marquis -- able to be checked with a hydrometer.
The battery will probably NOT be filled to the correct level when purchased, and it will probably NOT be completely charged.
An inexpensive, automatic battery charger will charge your new battery completely in a short time, usually within the time it takes to clean and prepare the battery compartment.
Before installing your new battery, wash the battery compartment thoroughly with plenty of water and Baking Soda (neutralizes acid spills and stops corrosion from spreading). Spray any corroded area with WD-40 before installing your new battery.
Check your battery cables and terminals and replace any damaged parts.
Connect your new battery, Positive cable FIRST, Negative cable LAST.

Good Luck ! !