OT.
While servicing my Zen at a MASS, I was told that the battery had to be replaced. I refused thinking that they were trying to fleece me as functionally my battery was great - starting at the first crank and no visible effect on the electrical systems.
But after a month, one day, drove to the office and while trying to start in the evening, the battery was dead. No warning symptoms of any sort. Had to push start the car and got the battery changed.
Lessons learned: It pays to heed to the service advice.