Why do you recommend replacing the battery if it has had no signs of deterioration - Just due to its age?

Yes, and it is NOT just me. The fact is, these cars (and MANY cars today) will not start or run right with a weak or questionable battery. My durango left me stranded, it would crank FINE, but as soon as I let go the key, it would die. They put a battery in, and it was fine. I paid a $80 tow bill, $60 diagnostic charge and $110 for a battery - LESSON LEARNED.

SO...............
My new battery cost $85 at O'Reilly's, I replaced it in the parking lot myself before driving all the way to the Dragon - I was NOT about to let a four year old battery ruin my weekend.

Oh, and if it IS four years old, you may not perceive any deterioration, but by that age, the battery IS NOT in the condition it once was!!!