Batteries have a typical lifespan of about 24 months b/c of the heat. In fact, that's what the battery testers @ Pepboys/Autozone/etc. will print out for you if you ask. I now buy Bosch-brand batteries... b/c they have a 36mos replacement warranty and a 96mos pro-rated warranty. I've had 2 batteries died on me (once in the Boxster (26mos) and the other in my Audi A4 (18mos)) and took them back to Pepboys, they look up my info, looked at the mfg date and gave me a brand new one at no charge. Just make sure you keep a copy of the receipt/scan it so the receipt ink doesn't fade on you after a year.
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