No outside power source needed; simply touch either the positive or negative side of battery to the corresponding contact point on the tester f

The Gardner Bender GBT-500A Analog Battery Tester is a reliable tool for testing batteries ranging from 1.5V to 22.5V with a wide variety of applications. It features an easy-to-read selector switch and a color-coded "Good/Replace" indicator. Additionally, a button cell retainer holds the battery in place for a more accurate test. Positive and negative contact posts on the front of the tester provide quick and easy 9V battery checks.

Tests: 1.5V Button cells, 1.5V AAA, N, AA, C, D cells, 1.25V Nickel-Cadmium rechargeable cells, 3V Lithium cells, 6V Lantern and photo light meter cells, 9V Rectangular, 12V, 15V Photo cells, and 22.5V Photo and lantern cells with Voltage Rating of 1.5V to 22.5V.