Maximising battery capacity

Steve Cassano — 23 November 2018

Many 4WDers and camper trailer owners have certain expectations about which standard extras will be included, or at least easily added, to their purchases.

It's not too cynical of me to suggest that many manufacturers like to pre-install a myriad of electrical apparatus and gadgetry that, hopefully, entices a straight purchase from the showroom floor.

I recall a time when many vehicles and trailers would be classed as luxury if fitted with an AM radio with twin speakers – and even then it was an option that you needed to tick.

Fast forward to today and there are heaps of cool and nifty electrical devices available. But what happens if your pride and joy is an older model, or you purchased it second hand? What if what you want is not easily available off the shelf?

Perhaps you simply want to customise your rig a certain way and save a few dollars? Perhaps your own design acumen and skill on the tools are the best way to achieve what you’re after?

After much personal trial, effort and the strong desire to get it right, hopefully I can impart a few pointers that work for me when it comes to adding and customising electrical options.


Like many older 4WDs, mine came fitted with very basic electrical accessories and features: a stereo and a few cigarette outlets in awkward places. These were also hardwired into the main electrical loom, which received power from the main starter battery.

I wanted to improve on what I had, to make my 4WD better for long distance touring: easier to use, dependable and safe. All this while making it independent of the main loom.

To make these fundamental changes, you have to first make a plan. Create a checklist of wishes and desired outcomes and use these to inform it. Having a solid plan will save you time (believe me – heaps of time and repetition) and, of course, money.

Take an all-encompassing approach to planning, even including things you may not get around to until far into the future. There's nothing worse than undoing days of work just because you want to add another single wire through you vehicle.

Once your plan is set and you’re sure of your needs, I suggest the following hardware and tools to successfully complete the task:


There's plenty of different battery systems you can run while camping, but one basic rule of thumb is that you need to protect and isolate the starter battery at all costs. When you add any accessory (apart from a winch), aim to run them off of an auxiliary battery. 

There are a variety of battery types and sizes to suit most applications. When you buy ensure it’s a deep cycle battery and when you install ensure it’s tied down and secured.

Due to the physical constraints under my 4WD’s hood, I opted for an Optima AGM battery, as they’re reasonably priced. Mine cost $320 for a 55Ah; yes, small by most standards, but adequate for my purposes. They’re proven, robust and typically have a long life. As well, they can be safely stored at any angle inside the cabin. My two current Optimas are four and seven years old and still work fine.

A DCDC charger will also help to maximise battery capacity and life; it will correctly manage your batteries, especially when it comes to newer vehicles fitted with voltage or temperature sensors (smart alternators).

Some, like my REDARC 1225D, come with in-built solar and can manage different battery types, such as; GEL, AGM and the new kid on the block, Lithium. It has performed superbly so far.

The REDARC 1225D output is rated at 25amps. It’s compact, solid, dust and water resistant and comes with many likeable features. They can be purchased for less than $500 if you hunt around. You will, however, require some fuses and extra cable to complete the job, which add about $80 to $100 to the overall cost. They’re best positioned within one metre of your auxiliary battery to ensure maximum efficiency.


Using a fuse box, rather than an array of separated fused cables, results in simplicity and easy analysis when required. There are many inexpensive fuse box styles available on the market. I opted for a six-way, as I didn’t anticipate needing to protect more that six accessories.

They retail for around $20 to $30. Each circuit is rated to a maximum 30 amps. Mind you, 95 per cent of what you may add rarely exceeds 10 amps but, please, check first. There are some units that can protect up to 12 circuits. The fuse box is best placed as close as possible to your battery in a dry, safe area and away from too much heat.

You can also benefit from incorporating switches into your setup. I chose the industry-preferred Carling-style switch. They’re standard sized and easy to configure and use. Heaps of designs are available to help indicate which device it’s managing. They can be either a simple on/off style or a momentary switch, such as that used for a horn or winch. They illuminate when on, or when in standby, and have many colour choices.

Many newer vehicles don’t have obviously convenient places to install switches. Well – not neatly anyway. Using a panel housing allows you to neatly install and nicely frame your switches. A panel housing will enable you to add more as need dictates and it finishes everything with a professional look.


As mentioned earlier, most requirements won’t exceed a 10amp draw, though there are some notable exceptions.

Some larger fridges exceed 10 amps, although even an older Waeco 110 uses only eight. Mind you, some fridges draw higher amperage on start-up and settle once cool, so take that into account. I use a 15amp wire for my fridge.

While LED lights profess to draw little power in comparison to their predecessors, they do increase their draw when facilitating the larger LED light bars or multiple LED strips on the same circuit.

Another common device, if you decide to hardwire it, is an air compressor. Air compressors tend to draw plenty of power, especially when working hard. A typical compressor, such as ARB’s single compressor, draws more than 32 amps and is fused with a 40amp blade fuse.

In short, power-hungry devices are better off with separate fused circuits to the auxiliary battery with a heavier gauge cable.

Naturally, where you need to connect your wiring, you’ll need terminal connectors. These connectors are inexpensive, insulated and colour coded red, blue and yellow, dependant on wire size, for less than $4 per packet. For heavier gauged cable, Narva lugs, at about $1 each, are my preferred choice and come in a variety of sizes.


To ensure proper electrical integrity, all connections must be secure. In order to affix your connectors, you could use basic pliers. Better still, get yourself a ratchet-style crimp tool for around $25. They’re easy to use and ensure a correct and secure hold. For the larger Narva style lugs up to 16mm², again around $25, get hold of a battery-style crimp tool.

While crimping will suffice for most of the connections, occasionally you may need to join wires together and the best way is to solder. Using a solder is simple if you follow a few tips.

I use a 60W iron, costing around $30, and 1mm of 60 per cent tin, 40 per cent lead, solder. Heat the wire, and once hot, keep the iron in contact. Bring the solder to the wire, not the iron. The hot wire will absorb the solder through the threads and ensure total coverage.

One of the very first tools I purchased was a multimeter. At first they may seem daunting to understand, but they’re an essential tool when doing any electrical work to your setup. While there are some excellent automobile-specific and comprehensive units on the market, even a basic unit – for around $10 – will do for a start. Multimeters perform a variety of tasks, such as testing: voltage, parasitic drain, amperage draw, connectivity and much more.


For those not familiar, heat shrink tube comes in approximately 1.2m lengths and a variety of colours and sizes for about $4 to $8. It’s trimmed to length to insulate or protect bare wires. It’s properties allow it to easily pass over the chosen area; then, you cast heat over the tube and it will shrink to form a strong bond.

For a few dollars more, I use the dual-walled version. It’s thicker, shrinks tighter and has embedded glue that oozes out to provide a more waterproof, stronger seal.

Having wires running throughout your cabin and under the hood, like spaghetti, exposes them to heat and possible wear from vibrations and contact with other components. Using spilt tubing (which comes in a variety of diameters) and cable ties ensures all cabling is safe and easy to manage. It’s viable to run multiple wires inside one tube, dependant, of course, on its diameter. Split tubing is a little pricey but don’t underestimate it’s worth. As for cable ties, well they’re everyone’s favourite, so buy heaps of them.


While working on electrical systems is not everyone's favourite task, it is worth at least investing a little time learning the basics. This is especially so if you travel to remote areas, wish to save a few dollars, or just want a better understanding of your vehicle’s attributes.


nuts and bolts technical electrical electronics battery camper camper trailer