Battery testers are devices that measure the characteristics of a battery, such as voltage and current, to determine if the battery is in good shape and functioning properly. They help a user to diagnose electrical issues, measure resistance/impedance, check voltage output and amperage, identify problems with charging systems, and monitor the battery’s health and lifetime. Battery testers can be used with the most common battery types, such as AGM, lithium-ion, and lead-acid, as well as a range of sizes, operating temperatures, and load currents.