The warranties on batteries vary tremendously by brand and battery type. At the most basic, warranties may be for a year or two; some of the best written warranties are for as much as 10 years. Warranties will usually include a free replacement period, followed by a prorated term during which a replacement will be supplied at a reduced price. The key to warranties, however, is that they are designed to cover manufacturing defects, not perceived overall premature failure due to poor maintenance and loss of capacity from sulfation. That is, if a single cell fails during the warranty period, the cell (or battery case with that cell) may be replaced under warranty. However, if the entire bank fails prematurely, it won’t be covered.