We purchased two Lifeline batteries in 2001. After only two years, one of the batteries failed. We contacted Lifeline, told them our charging and use patterns, and they sent us two new batteries at no cost to us—they even paid the shipping—and with no arguments. That’s standing behind your product!
Update, August 2010:
AGM batteries have continued to cause us difficulties. But, together with Lifeline, we are testing the best way for liveaboard cruisers to care for their batteries.