this product is fully functional, you can display the battery voltage, battery power, you can also plug directly into the phone or other 5V equipment charging. This product is suitable for all kinds of outdoor power, mobile power, instrumentation and other equipment additional battery power voltage display and additional USB to charge the phone and other functions. this product uses synchronous rectification step-down chip scheme, low heat, energy saving and environmental protection. This product is compact in structure, making full use of space and reducing costs. Static input current: 5-25mA, the lower the battery voltage, the smaller the current. USB output: 5V/2A (a USB setting for recognition, a setting for Android recognition) USB buck efficiency is up to 96% (because of the synchronous rectification circuit, the buck conversion efficiency is high and the heat is low. 8 segment power resolution: 10% 25% 40% 50% 60% 75% 90% 100% The accuracy of the voltmeter is about 2% working temperature: -10 ~ +65 ° C Working humidity: 10~80% (no condensation) Display Type: Digital Only Model Number: DL-USB-02 Operating Temperature: -10~65 Accuracy Class: 1% : Electrical Power Supply: DC12.6V Colour:black Size:45*26*18mm Material:plastic Package Contents: 4 * digital display voltmeter Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.