The Portable 12 Volt BatteryLevel Indicator shows thepercentage of the charge and hasa large illuminated, easy toread display.The battery level indicator isfor all types of 12 voltbatteries including auto, RV,marine, and motor cycles. It issimple to use. Just clip theblack lead to the negativeterminal and the read lead tothe positive terminal. Theindicator will show aundercharge or overcharge onyour battery.