IMHO, the average car battery lifespan is 5-7 years.
General Grant (87 560SEL) has an Interstate Megatron (their premium battery/"lifetime warranty" )
That vehicle is only driven on special occasions, otherwise sits in the basement on a battery tender.
I was getting uncomfortable with how old the battery was (11 years!) so I stuck it on my 1953 Sunnen load tester: 350A/10 seconds/9.2V! Very good/pass!