12 V 140amp Durite 0-727-33 Voltage sense Relay suitable for any type of leisure battery if using the correct size cables and especially suitable for all modern vehicles as you dont need to interfere with the vehicles electrical system.
Simply connect the relay between your vehicles main starter battery and your second/leisure battery and the relay will charge your secondary/leisure battery while you are driving and stop your main starter battery from discharging when you are stopped.
The relay simply detects the rise in voltage from the vehicles charging system when the engine is started to allow power to charge your second/leisure battery.
The relay will switch on at 13.3volts and switch off at 12.65volts and is indicated on with a red LED.
Please note that Durite have modified this relay to cut out at a lower 12.65 volts to enable it's use with some of the modern smart charging alternators.