Diehard is a premium brand of automotive battery marketed by Sears.

The brand dates to the 1960s. In its earliest years, the brand was guaranteed to last "forever", that is, as long as the original owner still owned the car in which it was originally installed, far more generous than traditional pro rata battery warranties. When drivers began to keep automobiles for longer periods than had been traditional previously (due to both their rising cost and hence longer financing contracts, and their improved durability), the cost of this policy became prohibitive and it was discontinued. However the brand line was kept and expanded; it now includes medium-priced, medium-duty batteries as well as the premium-priced, heavy duty line with which it was begun., and in recent years has been expanded to include other, non-automotive batteries as well. The recognizability of this Sears brand (along with other high-profile Sears brands such as Kenmore and Craftsman is given as one of the reasons for Kmart's desire to purchase Sears, which was publicly announced in November 2004.