The Gardner Bender Battery Tester checks if a battery is charged or needs replacing. The tester works for all battery sizes, including D, C, AA, AAA, N, 9 V rectangular, and button cells. It is small enough to fit in a pocket and comes with a one-year warranty, so you can be confident in its ability to test your batteries. Gardner Bender has 50 years of experience making professional electrical tools and supplies of consistently superior quality, so you can count on high-performance products at a fair price.