4x4

Being in Charge with Dual Battery Management: Part 1

A touring 4×4 needs more than its single battery, but how do you go about setting up for dual batteries?

LIKE MANY AVID 4WD owners who like to travel whilst still accessing the odd electrical powered devices when away from the grid, I looked for the best solution to provide ample power for all the extra modifications and accessories.  My basic criteria were; the solution had to be reliable and effortlessly exploit the full potential of my 4X4’s power plant, and it needed to be easy to implement and use.

These days most modern 4X4s have, at the heart of their electrical system, batteries that are quite reliable, have a reasonable capacity to provider electrical power to a 4X4 in standard trim, are properly secured and built to provide enough cranking power to turn over the engine and start all those electrical computers and sensors.  These batteries are more than adequate for the average 4X4er who prefers to remain within sight of the city lights and not add anything substantial to their vehicle.

Previous set up using a simple Projecta solenoid but not delivering 100% charge to the auxiliary battery

Initially, in my case, I knew that I wanted to address 3 requirements but this soon changed to 4 after intensive deliberation between my brain and wallet as well as support specialists.

  1. Extra capacity to avoid overloading the main battery. Firstly, I knew that I was going to put additional strain on my standard battery and that the capacity may not be enough to ensure successful and prolonged use of any extra accessories that I had. The worst case scenario was a flattened starting battery if the vehicle wasn’t getting regular drives to top up the battery via the alternator.  Naturally a flat battery in a remote area is not a good thing, especially for an automatic, whereas a manual car “maybe” able to get going, either clutch starting downhill or being towed behind another vehicle.
  2. I wanted some form of redundancy. Example in the case that my starting battery did actually go flat (e.g. running stereo or inadvertently leaving electrical devices plugged into the main wiring system too long), or unanticipated failure of the starting battery due to age, collapse of the internals or external damage.  I also wished this to be as simple as possible, so I could set it in place and trust that it would work as expected.
  3. An easy swap. This requirement follows closely from the previous as I also looked for the easiest way to swap another battery with the main starting battery, without major reconfiguring of their positions or the battery tray mounting or major rewiring of the electrical cables. If both batteries are the same, then this is easily achieved.
    If they are the same type, it also gives me the ability to easily pair them in parallel, thus doubling my starting battery’s capacity.  Parallel pairing is simply connecting positive from one battery to positive of the other and negative to negative.  I carry a short 2B&S cable with connectors for this purpose.  The circuit remains at 12V, (actually, rarely are they exactly 12V, depending on 4WD model).  This is especially advantageous for extended powering of my electric Warn winch in difficult circumstances.  My Warn XD9000 winch can draw up to 400Amps and I prefer it to be connected to the starting battery.
  4. Solar top up. this fourth and final requirements was added at the last moment even after I assured myself that my plan had been set in stone. I was swayed to add this requirement/feature after speaking with the experts in battery management at Redarc and after thinking of scenarios where I needed a constant power supply if I remained in one spot for too long, such as lengthy camping breaks or worst case, I was immobilised for extended periods.  This led me to exploit the sun to provide power to top up my battery system and not just rely on running the Jeep’s alternator.  Once again I wished it to be easy to use, compact and as automated as possible.

What I needed to work for my Wrangler

In late 2012 when I purchased my Jeep JK Wrangler, I had great plans and expectations from the iconic 4X4.  One of many expectations was to add several power-driven accessories such as a winch, fridge, LED lights and extra outputs to plug in GPS, phones, tablets etc. and curtail any battery failure or inadequacies.

Like most seasoned 4WD owners, the solution was to install a dual battery systems (starting  battery and an auxiliary battery) that would suit the Jeep and tick off my four requirements.  But as I found out soon enough, not all systems suit all vehicles.

– 2 x Optima batteries secured and with 2 B&S earth cable, before connection to DCDC Charger

There were three things I needed and they all had to work together seamlessly:

1. Buy a battery tray to accommodate the auxiliary battery separately from the starting battery or a tray that can hold the two batteries side by side.
Fortunately to have both batteries under the hood, Uneek4x4 had just released a double battery tray specifically for the 2012+ Jeep Wrangler.  It allowed two batteries to be positioned in the same vicinity as the original stock battery with no changes to the original battery cabling.  With easy to understand instructions and some minor modifications to the surrounding support structures, I was able to slot in a very durable and well-built battery tray under the hood after parting with around $320 and about 3 hours of my time.

2. Add a deep cycle battery to complement the original starting battery or purchase two identical batteries.
With my chosen battery tray, there was some restriction as to battery size and type that would fit. While the tray maximised available space, it did restrict the size of the batteries that could fit.  It had been designed to hold two D34 group Optima Yellow Top AGM Batteries of 55amp capacity each.  These Optima batteries are an unusual style, in that they are designed to be a starting and deep cycle battery.  They have a great reputation to handle excessive heat and abuse plus push 750CCA to start up the Jeep with ease.  While expensive at around $320 each, I knew they were perfect for my needs and met my requirements and would last for many years.

3. Select a system to manage the two batteries, associated wiring, fusing and layout.
With all dual battery systems, the starting battery should be dedicated to starting the vehicle. The exception in my opinion is connecting an electric winch as it only runs while the engine is running. The auxiliary battery is left to cope with all the accessories such as fridges, lights etc. and act as a backup in case of a starting battery failure.

Original Basic Dual Battery System

At first I had utilised an old Projecta DBC150 amp solenoid that I had left over from a previous 4X4.  Briefly, the Projecta solenoid has two connectors which used 185amp cables to each battery’s positives.  It priorities current from the alternator to the starting battery and only switches to the auxiliary once the starting battery is full (well not really full but perhaps 75%, hence why I sought a DCDC solution, but more on that later).  It also allows a jump start between the two batteries with a push of a button.

While the solenoid did a reasonable job, it became apparent soon after that it didn’t maximise the full potential of the dual battery system and eventually failed to work due to age.  I then began to research the latest battery management choices.

Just the place to fit a Dual Battery manager – Very tight but in the coolest place I could find

After plenty of research I came to the conclusion that a DCDC in-car charger was the best option.  When it comes to my 4X4I prefer to implement well-known brands that have a good reputation for quality and service.  I also try where possible, to buy Australian products.  I had narrowed down a couple of companies that stood out with their reputation, well recognised quality build, variety of options and were Australian made.  Though after phoning their support, I soon discovered that they would not recommend their DCDC charger in my case unless the battery was a minimum 75amp.  As mine was 55amp Optima battery, I was left with just one company and that was Redarc.

Next time I’ll talk further about DCDC chargers, the reason I chose Redarc and my installation.


Steve Cassano

Steve Cassano

Since 2010, I've attained various qualifications and experiences to deliver Accredited and Defensive Driver training to the resource and recreational sectors. I've written many 4WD articles for various 4WD and SUV magazines which I find very exciting. For nearly 20 years, I've been a very passionate 4WD owner who loves to travel remote areas as well as hit the tough tracks near my home town of Sydney