Dynatek Charge Monitor DCM-1 Allows user to track electrical system voltage on any vehicle with a normal 12V charging system When the normal green light is on, the system voltage is normal and the battery is being charged correctly; if the high red light is on, the system voltage is too high and damage to the battery may result; when the low red light is on, the system voltage is too low and the battery is being discharged The above indications are valid only with the engine running Measures 15/8in L x 1in W x 1/2in H