Because lithium batteries, such as RAYOVAC®'s 9-volt battery, operate at a relatively constant voltage level throughout their life, and do not decline significantly in voltage until they are near end of life, it is not possible to use a battery tester to determine if a lithium battery is still good. For this reason, there are no testers available for use with lithium batteries.
When viewing the voltage curves, you will notice that, depending on the cut-off voltage of the device that the battery is powering, (e.g., a typical device's low voltage alarm might be 7 volts) on average the lithium battery outlasts an alkaline battery by 2 times.
Because it is not possible to use a battery tester to determine the remaining life of a lithium battery, we suggest you run some tests comparing the actual life of alkaline vs. lithium batteries in your devices. Once you determine the lithium battery life under typical usage conditions you can then implement a battery change program based upon the amount of time they have been in use. For example, if you determine in your testing that the lithium battery outlasts an alkaline battery by 3 times, and you typically change alkaline batteries once a day, you can then change the lithium batteries every 3 days. You can modify that change schedule depending on how often the devices actually go into a low battery alarm condition. In this way you will get the most value from using lithium batteries.