No electricity required: universal battery tester is activated by the battery to be tested, so no batteries are required for operation. Thanks to the adjustable slider, the battery tester is compatible with most batteries and button batteries. ACCURATE TESTING RESULTS:The digital battery tester is faster and more accurate than the average battery tester. You can use it to determine the battery consumption without having to wait. Easy to read: the digital display immediately shows the battery capacity. Behind the product there is a overview chart, you can see the performance of all types of batteries at a glance compared to the numbers on the back. Displays exactly the voltage on two decimal places. Easy to use: check whether the battery touches the two contacts of the tester, and read the numbers on the LCD display. You can decide whether you need to replace the battery using the current power status of the battery. Measurement fits the measurement with a multimeter. It does not need an internal battery, Easy to carry: the LCD battery tester is a simple and effective battery tester, suitable for AA, AAA, C, D, 1.5 V, 9 V and button cells. The small and lightweight so you can use it in daily life and travel. In terms of the problem that the display is not displayed, please check if your battery is completely unusable, and then contact us to solve the negotiation method.