Battery lifespan

Had to change the battery on the 04 Lancer ES today. First time since new.
NRMA bloke told me that a normal battery for me car has about 350amps and
my one was reading 88amps. So time to change.

I was also told by another fellow that a 3yo battery is due for
replacement
anyway. I tort they lasted a bit longer than 3 years, say 8years or so? Or
am I too optimistic? :)

I can't stop trolls from getting into this post but I am genuinely
interested in battery lifespans in a motoring sorta way :)