Reverse polarity protection: even if the positive and negative connections are reversed, the device will not burn. Simply correct the wiring. Realtime battery level display: connect the display board to the tested battery, then press the red button to illuminate the LED and show the current battery level. Easy operation: a single red button provides a quick, intuitive read of the battery status without complex setup. Low idle power consumption: after you release the button, wait 3–5 seconds for the LED to turn off; when off, the unit does not consume power. Simple connection steps: connect the positive terminal of the display board to the positive terminal of the tested battery, and connect the negative terminal to the battery negative. Practical use scenarios: Field testing of battery packs for electronics hobbyists, technicians, or DIY projects to verify remaining charge quickly. In a or assembly workshop, to confirm battery status before powering through a device under test. In a laboratory setting, to perform rapid, noninvasive checks of battery conditions during experiments or demonstrations. Performance and compatibility notes: Designed for straightforward connection to standard battery terminals via the display board. LED indicator provides a clear, realtime readout while the red button is pressed. Power is used only during LED illumination; no standby power draw when not in use.