Using a Hardkorr battery box with voltage-sensitive relay (VSR) is the simplest way to create a dual battery setup in your vehicle.

The VSR acts as an isolator, allowing the auxiliary battery (inside the box) to charge directly from the crank battery while the alternator is producing at least 13.2V (i.e. the engine is running). When the ignition is switched off and battery voltage drops below 12.7V, the VSR automatically cuts the link between the auxiliary and crank batteries to prevent the crank battery from being discharged.

Our optional dual battery wiring kit makes it an easy DIY job to install your dual battery setup.

This Voltage-Sensitive Relay can also be used in 12v setups without a Hardkorr battery box.

PLEASE NOTE: this product is not suitable for vehicles with a variable-voltage alternator OR Lithium Batteries. Please check with your vehicle manufacturer prior to purchase if you think your vehicle may be equipped with a variable voltage alternator.

This plug-and-play dual battery wiring kit makes it easy to turn your Hardkorr Heavy Duty Battery Box into a dual battery setup. It is designed to work in conjunction with our Voltage-Sensitive Relay, or can be adapted to work with a DC-DC charger as well.

This kit contains everything you need to wire up your dual battery setup (other than the VSR/DC-DC charger), including 6 metres of high-quality 8AWG cable and a 50A maxifuse.