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DIY Build a Portable Dual Battery System.

Article by Steve Smith - Caravans Plus

Dual Battery Systems are a must have for any serious traveller. They allow you to use your 12 volt power without risking a flat starting battery. However there can be many reasons why a second battery under your hood is not the best option.

I have a Prado with LPG and there is not enough space to have 2 batteries in the engine bay. I ended up putting a really neat second battery in the back. It works so well and was so easy that I wanted to share the exact method I used. Best of all my second battery is fully portable and the whole thing only took 1 hour and cost me about $850. It was much quicker and cheaper than taking it to the pros and I think a better result.

Isolator

Dual battery systems basically work because the second battery is connected or separated from your starting battery with an isolator. When your car is running, the isolator connects both batteries together and allows them to charge. When your engine is off, the isolator separates the batteries. So if you do manage to flatten your second battery you will still be able to start your car.
I installed this simple little isolator (shown below) in my engine bay next to my starting battery. A short piece of thick wire from the positive (+) on my starting battery to the positive (MAIN) on the isolator is all that is needed. The negative connection is the earth to the car.

GSL Smart Battery Isolator 100Amp - 12v

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Auto Wire 8mm Single Core, Suit-12V Winch 100amp, Per Metre

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Charging cable

Once the isolator was installed, I ran a few meters of wire from the isolator (AUX) to the back of my car. This is the positive (+) you can get the negative (-) from the earthing to the car again. I attached an anderson plug to the end of the wires. 12 volt wiring is quite simple and you do not need to be an electrician, just remember to keep your batteries disconnected while you play.

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Second battery

Thats all the tricky part done! The actual portable battery system is a ready made unit that you just need to plug into that anderson plug you now have in your boot. I ended up using a box called the ARKPAK. It cost me more than some other products, but it has so many more features like LCD battery monitor, built in 240V AC inverter, USB charger, and cigarette outlets. It also just looks a lot neater than anything else I could find. You can add any battery to the ARKPAK, I used a large deep cycle battery. This one is sealed which is important since the box is inside the vehicle.

ARKPAK Battery Box. 12V & 240V output, AP620

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Camec Deep Cycle 120ah AGM Sealed Lead Acid Battery

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This portable dual battery system has been great for me. I have a 12V Waeco fridge and some lights that I plug into the ARKPAK. It will run my stuff for about a week before I have to put it back in the car and go for a drive. The ARKPAC is also set up to be charged by solar panels - so thats my next project!

Worth a mention

I have seen the ARKPAK has a built in smart charger but it is bypassed when using the anderson plug. This means it charges the same way as your starting battery.

Unlike some under bonnet dual battery systems, if you somehow get a flat starting battery you cannot directly start your car from the ARKPAK. You would need to pull the batteries out and swap them around or use jumper leads.

Was this helpful?

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2 Comments

  • comment-avatar

    paul

    Great article and most helpful - thanks .

  • comment-avatar

    Clive

    What a great article& so simply put, even for a layman

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