1, this product is fully functional, that is, it can display the battery voltage, battery power, but also can be directly plugged into the mobile phone or other 5V devices charging 2, this product is suitable for all kinds of outdoor power supply, mobile power, instruments and other equipment additional battery power voltage display and additional USB to charge mobile phones and other functions. 3, The front is the on/off button, the back is the setting button, please set the parameters before installing and using. Ternary lithium battery L measurement: Charge type: L03 string to L07 string (power-off memory) Lead-acid battery P measurement: Charge type: DC12V, DC24V (power-off memory) Iron-lithium battery F measurement: Charge type: F03 series to F08 series (power-off memory) Parameter: Dual USB type Power supply voltage: DC8-30V Measuring range: DC8-30V Colour:black Material:ABS Size:47.6 x 28.7 x 19.4mm Package Contents: 1 x voltage meter Only the above package content, other products are not included. Note: Light reflection 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.