In our case we got 17 months out of one fob's battery and 23 months out of the other. I believe we got a "low battery" warning on the dash display for several days before changing them and the range was noticeably weaker before changing them so there's plenty of advance notice. I don't plan to change mine till I have to for the simple reason that those clips in the fob don't feel like the most sturdy things ever and I don't want to stress them more often than I have to.
Gotta be careful what I post!!
Today my fob would not work
Took off cover and jiggled the battery a bit and voila... the remote worked to unlock and lock... I was just adding windshield washer fluid so did not drive.
Anyways at least it seems the fob can be reinvigorated. Strange as no warning on dashboard so perhaps a little jiggle was just needed for now.
Now to find best price for battery so not caught off guard!!
In case it helps... Wish we get a Billion dollars!!