I've seen posts on the Forum that indicated a battery life of around 10 years.

I usually work on the premise of "if it ain't broke. then don't fix it".

At $90 bucks a pop, I'd wait for the battery to die, or the unit to go belly up, before replacing.

(You should be able to buy them online for cheaper, but they still would have an install cost, unless you do it yourself)...