Most of these warranties don't refresh with the replacement, they stick to the original purchase date. Thus if there is a 3 year warranty and the batteries die after 1.5 years, you'll end up getting 1 free replacement but it doesn't continue forever, when that second one dies just after 3 years you get nothing. They're only guaranteeing you 3 years of working battery with the original purchase not that each battery will last 3 years specifically. I'm not saying they won't either, just pointing out how those types of warranties work.
