A bit ironic considering that earlier I mentioned that my wife's Mercury
Mountaineer had never had any issues (although this is only to be expected).

I was at the store this afternoon and she called me. Said, "On your way
home could you pick up a starter for my car?"

Obviously I asked her why she thinks she needs a "starter".

Her reply: "Isn't that what starts the car? All it does right now is
click."

Long story short, went home, checked the battery. Reads under 8 volts.
Pulled it out, went to AutoZone, bought a new one and all is fine.
Just for additional assurance, she's going to stop by AutoZone on Monday
for a free alternator check to make sure it's ok.

I was thinking about this. Unlike the "old days" before fuel injection
and electronic ignition, batteries today give very little warning that
they are about to give up the ghost. The old cars had to turn over a
few times to start (especially when cold) and a battery starting to go
south would give fair warning with sluggish performance. Now-a-days,
they can be fine one start-up and dead the next.

Her battery was less than 4 years old. She does a lot of short distance
driving everyday, starting, stopping, starting, etc., and not driving
very long between stops. This probably contributed to a shortened
battery life.

Then I realized my truck is over 6 years old and still has the factory
battery. It's a little heavier duty because the truck has the factory
"plow" package but I think I'll replace it soon anyway. They just don't
give any warning signs.