Voltage Sensitive Relay

Voltage sensitive relays. 12 Volt 140A with red LED indicator. Allows split charging of a second battery, without discharging the primary/start battery. For the 12V version, the relay makes at 13.3V and breaks at 12.8V. 

(For the 12V version, the relay follows the voltage, above 13.3V it switches in, and connects the secondary battery to the charging source. If the secondary battery is flat/heavily loaded and the charging source too lowly rated or the engine/alternator rpm is too low, the voltage can drop below 12.8V and the relay opens. With the load removed, the voltage recovers, the relay switches in and the cycle repeats. If this happens, increase the engine rpm or increase the rate of charge from the charging source).