A dual battery setup is essential to anyone who wants their vehicle to run a heavy electrical load, without being left with a dead starter battery.
They’re especially common in four wheel drives that have been set up for camping or exploring the great outdoors where a fridge needs to be run.
Installation is easier than you may think and only requires a few small modifications to your car or four wheel drive.
What you'll need
- Dual battery kit
- Second battery
- Drill & bits
- Marker pen
- Crimping tool
- Heat gun
- Diagonal pliers
Step 1 - Mounting The Second Battery
Start by deciding on a mounting position for the second battery in your engine bay. Supercheap Auto sell battery trays and all necessary accessories for mounting your second battery.
Just be careful to ensure your battery kit has enough wire to reach the second battery.
Step 2 - Disconnect The Main Battery
Disconnect the negative terminal from your main battery before starting any more work.
Step 3 - Mounting the VSR (Voltage Sensitive Relay)
The Voltage Sensitive Relay or VSR is the computer controller for the 2 batteries and needs to be mounted where it will be easily accessible. Away from any hot or moving parts and as close to the main battery as possible.
Use the mounting plate on the back of the VSR to mark and drill four holes, and secure the top right and lower left holes with the short screws. Then, take the length of red cable with lugs at both ends, and measure out enough cable to run from the centre of the mounting plate to the positive terminal of your main battery. Follow existing wiring where possible and avoid hot or moving parts.
Step 4 - Cut Cables To Length
Cut the cable to the correct length and repeat this step this time to the positive terminal of the auxiliary battery.
Fit the lugs to the bare ends of the cable by stripping away 15 millimetres of insulation and crimping them in place with the crimping tool.
Slide the heat shrink over the lug and heat it with a heat gun to give it a waterproof seal.
Step 6 - Attaching VSR earth
The black wire attached to the VSR needs to be earthed.
NOTE: It’s important that these earths are grounded securely; where possible use a bolt which has been used to earth the engine or other engine component.
Step 7 - Connecting The Main Battery To VSR
The cable from the main battery goes to the VSR terminal marked with a red dot, and the words “positive sense battery”. The cable from the auxiliary battery goes to the terminal marked with the words “positive second battery”.
Step 8 - Earthing The Second Battery
Your secondary battery will need a solid earth as well. Take the 24 inch black earth cable and again secure to a factory engine ground or similar.
Step 9 - Attaching The VSR To The Mounting Plate
The VSR can now be attached to the mounting plate using the two longer screws, and the positive cables may be attached to the main and secondary batteries.
Step 10 - Attaching The Negative Leads
Then secure the negative terminals - first to the main battery, then to the auxiliary battery. Use the cable ties supplied to keep your wiring neat and safe.
Step 11 - Testing The New Dual Battery Kit
If you want to test your new setup, you can do so with a multimeter. Start the vehicles engine and take a reading from the main battery. Once the voltage climbs above 13.3 volts, you should hear the relay click and the red light illuminate; to show that the second battery is connected. Now turn off the engine and take a reading from the main battery again. Once the voltage falls below 12.8, the relay should disconnect. To speed up this process, you may wish to switch the headlights on. If everything works as per these tests, you have successfully installed your own dual battery kit.
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