I replaced the battery for the Cummins 6.7 in my motorhome last year for the first time. I was installed in the chassis in late 2012. It was still working but I replaced it just to be on the safe side. I only use one battery for the Cummins since I replaced the other with capacitors that should last forever and actually produce a better starting jolt. The truck battery that I put in only cost $75 from the Kenworth dealer, seemed like a real bargain to me. I didn't mind running that the old battery a little longer than normal since I have a big set off house batteries already wired in for backup if needed.
I had a KMart lifetime battery in my 1970 Impala. I think that I got it replaced 4 times before some idiot stole it not knowing that it was already getting weak. He should have waited a few more weeks. I averaged right around 4 years per battery.
I had a lifetime battery from Honey's auto parts but on the third replacement they gave me a choice of a full refund or a non-warranted replacement, ending he warrantee either way.