When you have a box of used batteries, you want to know which one is still alive and which one is half dead. With the low level battery, it can still run your radio for a while, to save and keep least wast, you need a battery tester to decide which battery should go to trash can. This BT168 is designed for this purpose. You can check regular alkaline AA, AAA batteries, It checks 9V battery to give you an idea of good or bad. It check your watch battery too, any toys battery like C, D size 1.5V and rechargeable batteries. It is easy to use and compact to carry. It gives direct reading from analog needle. and red or green region to tell you it is good or bad.