After reading the various reviews I decided to purchase this tester. As soon as I received it I 'tested the tester', as some reviewers didn't rate it well. I knew I had a batteries that were weak (based on the device), worked but were used, and new batteries.The tester shows a variable range of power (with good, weak, & poor ranges) and accurately reflected the weak battery (based on my device use) as weak, the less used battery in low end of the good, and new battery as a top good readings. WheSee full review