LOL! If you can put a "for sure" life-span on a battery, you'll be the 1st person in history to be able to claim that distinction.
There are so many variables that come into play it boggles the mind. Couple that with the choices of..Lead Acid, AGM, Gel Cell, Lithium, Etc..Etc.
I just retired a lead acid OEM from my pick up this year..it was 13 years old...and the reason I retired it... I was in fear it was going to die out in the middle of nowhere, and leave me stranded.
Conversely, I have had batteries short between cells and die when less than 6 months old.
Best advice....buy good batteries, treat them according to the manufacturers recommendations, employ good maintenance and operating practices, and take your chances.
Oh, and Mutt....don't forget...it takes at least 9 volts to power the ECM reliably and allow the bike to start.