have 2 99 crown vics, and 1 99 grand marquis.
all 3 of them the battery will die if left sitting unused for more than 5 days, and on my P71, it has a mind of it's own. i can drive 500 miles, shut the car off and it will not restart. but then i jump start it, idle it for 2 minutes, and it is like a new battery was put in. it may work fine for weeks, or die again the next day. and this is with new batteries in all 3 cars, and a new spare i swap into them when one dies.