I got 8 months out of a battery that had a 3 year guarantee. I took it back to Supercheap Auto with a printout of it's failure details. They got very argumentative about replacing it. I said that's fine, write your name here on the small claims court document I had with me. WOW, was this chick angry. What with a queue of people laughing at her - I thought she was going to punch me. But I did get a replacement battery
Next time I'll pay a bit more and buy a Panasonic brand car battery.