The expected lifespan of a vehicle battery is minimum of 5 years.
Really? Where did you dig up that "fact" from. If you get 5 years out of a battery then you are doing well. Anything over 4 is a bonus. The OP's battery lasted 3.5 years... that's not too bad. He could be doing lots of short trips.
Century batteries offer a 3 year warranty on all new batteries. That means they expect that battery to operate with in its manufactured specifications for at least 3 years. With reasonable use one would expect to gain a further 2 years use out of a battery. Thats what i was told at VW where i sold 5 batteries a day. Am i asking too much?
No you're not. I must have had a phenomenal run of good luck, having only ever replaced 1 battery after owning about 8 cars. Two of which were purchased second hand and sold with the same battery in them after 7 and 8 years respectively.
Are you people really needing to replace your batteries every 3-4 years?? Is it because my most modern car is 1998 and the old fashioned batteries last longer or something?