Once your main starter battery is sufficiently charged, it will begin charging the second battery. 

• A voltage sensitive relay (VSR) is the best way to ensure you can always get your dual-battery vehicle started.
• Surface or panel mount options provides flexibility when installing.
• No voltage drops comparing to battery isolator diodes (0.6V).
• It has a solid glass fiber reinforced nylon shell.

Specifications:

Material: Nylon

Colour: Black

Size: 7 * 7 * 6cm / 2.8 * 2.8 * 2.4in

Nominal Voltage: DC 12V

Combine / Open Voltage: DC 13.3V / 12.8V

Continuous Current Rating: 125A

Intermittent Current Rating: 140A

Power Consumption: 10mA (Standby) / 330mA (Engage) / 0mA (Storage Mode)

Certification: CE IP67

Package Weight: Approx. 234g

Functional Features:

After the engine stalls, the left House battery discharges to the upper left load device, and the VSR disconnects when the battery voltage drops below 12.8V. The Start Battery on the right will not discharge to the device. When the battery on your left is not charging, it is used up. At least there is a little battery on the right that allows you to start the engine.