CD-i member Johan Veenstra showed us his CD-i player that he owns since 1995 and the timekeeper battery is still running. I can confirm this with my own CD-i 450 player, which is also running since 1994 and the timekeeper battery is still alive. That's 25 years of service! What I hear from experiences after repairing an empty battery is that the quality of the current stock is not that good, but it depends on the circumstances these chips are stored in. If you treat them nice, in low humidity and normal temperatures (not too cold and certainly not too hot) these chips can, even when activated like in this player, hold up for 25 years.
[Thanks, Arcadegamer573]