Dual battery system

- plus -

Redarc DC-DC Charger

LandCruiser 200

Step-by-Step installation

An efficient battery system is essential for outback touring, and while the LandCruiser 200 has dual batteries as standard, they aren't set up ideally for camping or touring use.

This article will cover the modification of the 200's standard battery setup by splitting of the factory dual battery system into a single battery for starting and factory loads, plus a deep cycle battery dedicated to accessories, charged via a Redarc DC-DC charger.

Affiliate link notice: This page contains eBay affiliate links, for which I may receive a commission if you click on a link and make a purchase of any item on eBay. The price you pay is unaffected. 

Upgrading the dual battery system in a LandCruiser 200

Although the LandCruiser 200 comes standard with dual batteries, they are permanently connected in parallel, meaning they effectively operate as one single, large starting battery. This isn't ideal for touring as it means an accessory load (such as a fridge) drains the starting batteries.

The solution is to 'split' the batteries into one dedicated to starting the engine and supplying factory loads, and a second battery dedicated to most of the aftermarket accessories. The starting battery continues to be charged directly by the alternator, while the accessory battery is charged using a DC-DC charger.

There are many different choices in battery and charger types to achieve varying outcomes, depending on your needs and vehicle setup. In my case, I have chosen a Century Overlander 4WD-Optimised lead-acid starting battery, together with a Century flooded lead-acid deep-cycle accessory battery, and a Redarc BCDC1225D with solar input (Also available on Amazon). The Redarc charger will be mounted using a purpose-designed bracket, sold by REDARC and made in Australia by The Long Ranger/Out Of Town 4WD.

 Starting batteries

Because you're dropping to a single battery for starting the vehicle, it's important to choose one which can supply sufficient current. This is shown on the battery as the CCA rating. I recommend at least a 650CCA battery for the 200. In my case, the starting battery will also power the electric winch and the Fyrlyt Nemesis driving lights. There are a number of options available for the starting battery, with pros and cons for each:

A 4WD-optimised lead-acid battery

These are similar in basic construction to standard lead-acid batteries, but have additional features to improve vibration resistance, such as fibreglass matting between the plates. They also offer superior cycling capability to standard batteries, so they can tolerate higher levels of discharge. The Australian-made Century Overlander N70ZZLXHD that I have chosen is an example of this type of battery.

  • Pros: High CCA rating (730) for good starting and also ideal for winches; Semi-cycling capability; Superior vibration resistance to standard lead-acid.
  • Cons: Slightly more expensive than a standard lead-acid battery.

An Optima Yellow Top AGM battery:

Optima batteries are an AGM battery with spiral cells rather than the flat plates used in most batteries. They are fully sealed and extremely resistant to vibration. The red-top versions are for starting only, and I don't recommend them. Yellow top and Blue top are dual-purpose starting and deep cycle. If you go with an Optima, the version most suitable for the 200 starting battery is the D31A Yellow Top.

  • Pros: Very high CCA rating (900) for good starting and also ideal for winches; Deep-cycling capability means damage-resistant if discharged excessively; Designed for high vibration resistance; Maintenance-free.
  • Cons: Much more expensive than a standard lead-acid battery or 4WD-optimised battery; 25% lower Ah rating than similar-size lead acid batteries.

A standard lead-acid battery

These are the typical starting batteries used in most cars. An example is the Century N70 High Performance range.

  • Pros: Good CCA rating (700-720) for good starting and also ideal for winches; Cheaper than the 4WD-optimised batteries.
  • Cons: Shorter lifespan in harsh conditions; More likely to be damaged by heavy discharge (eg extended winching)

 Accessory / Deep Cycle batteries

The second battery in the 200's engine bay, located on the right hand (Driver's) side will now be a dedicated accessory battery. Typically, deep cycle batteries are specified for this type of use, and they are rated in Amp Hours (Ah). This battery will run all the aftermarket accessories in the vehicle, with the exception of the electric winch and the driving lights. There are even more options available for this type of battery, but there are some significant pros and cons for each:

A flooded deep cycle battery

This is the type of battery I have chosen, specifically an Australian-made Century N70T. Flooded deep cycle batteries use traditional lead-acid chemistry, but in a design that's specially designed to cope with regular cycling. The N70T is designed for under-bonnet use and has construction features to resist vibration.

  • Pros: High Ah rating (100Ah); Suitable for under-bonnet use; Superior vibration resistance to standard lead-acid.
  • Cons: Not maintenance free (ie requires topping up).

An AGM or GEL deep cycle battery:

AGM (absorbed glass mat) or Gel deep cycle batteries are commonly used for accessory applications, but they have one major drawback. With few exceptions, they do not operate well at high temperatures, making them unsuitable for under bonnet use. Unfortunately, this limitation is rarely mentioned on sale listings. They are a good choice for caravans and trailers and for a 3rd battery located within the vehicle.

  • Pros: Good Ah ratings; Maintenance-free.
  • Cons: Not suitable for underbonnet use.

An Optima Yellow Top AGM battery:

Optima batteries are a special AGM battery with spiral cells rather than flat plates. They are fully sealed and extremely resistant to vibration. Yellow top and Blue top are dual-purpose starting and deep cycle. The version most suitable for the 200 accessory battery is the D31A Yellow Top. Their major drawback compared to other deep-cycle batteries is a roughly 25% Amp-hour deficiency for similar physical sizes.

  • Pros: Very high CCA rating for good starting and also ideal for winches; Deep-cycling capability means damage-resistant if discharged excessively; Designed for high vibration resistance; Maintenance-free.
  • Cons: Much more expensive than a standard deep cycle batteries or 4WD-optimised batteries; 25% lower Ah rating than similar-size flooded lead acid, AGM or Gel batteries.

A 4WD-optimised lead-acid battery

The 4WD-optimised Century Overlander that I have chosen as a starting battery is also somewhat suitable for use as an accessory battery, depending on usage. If you plan on running a fridge for extended periods without charging (ie: deep-cycling the battery), then this type of battery is not ideal.

  • Pros: High CCA rating means you can use it to jump-start if the starting battery fails; Suitable for running an electric winch; Superior vibration resistance to standard lead-acid.
  • Cons: Not suitable for true deep-cycling.

 DC-DC Charger

One of the side-effects of splitting the batteries is that the 'accessory' battery is no longer charged directly by the alternator. In the past, this was commonly overcome through the use of a battery isolator (allowing the alternator to charge both batteries, while separating the loads). However, this method is rarely used any more. Using a DC-DC charger offers several advantages over an isolator, including:

  • Allowing mixed battery chemistries: Lead-acid, AGM, Gel and (particularly) Lithium batteries all have different ideal charging profiles. Charging mixed types of battery with a single alternator leads to poor charging of both batteries.
  • Improved battery life: The ideal charging profiles used by the DC-DC charger extends the life of the battery compared to direct alternator charging.
  • Solar charging: Most DC-DC chargers provide secondary inputs, allowing you to connect solar panels to charge the battery while the engine isn't running.

Choosing a DC-DC Charger

There are a number of brands of DC-DC charger available, but for my money there's only one choice: REDARC. Their products are designed and made in Australia for our very harsh conditions and their reputation for reliability is unrivalled. The Redarc chargers operate down to input voltages of just 9 volts, while most of the Chinese chargers only operate down to 12.7 volts. This is particularly important when the chargers are mounted away from the main battery (such as in the rear of the vehicle or in a trailer), with solar charging and with some modern vehicles that feature "smart" alternators.

I've decided to go with the 25 Amp version of their dual-input 12 volt DC-DC charger, the BCDC1225D. This is ideal for the loads I will generally be imposing on the accessory battery, and for its 100Ah capacity. If you plan on having higher loads (such as running multiple fridges, inverters etc.), and/or you have a higher capacity battery (eg 200Ah), then you should consider the higher capacity BCDC1240D. For the ultimate in battery management and detailed remote monitoring, consider a battery manager such as the 15A BMS1215 or the 30A BMS1230. I have the 15 Amp version in my camper trailer, and it's very hard to think of a better charger in that application.

Why move the winch and driving lights to the starting battery?

As part of the installation, I'm relocating the power source for the electric winch and the driving lights across to the starting battery. The reason for doing this is simple: Current draw.

An electric winch can draw 400 amps or more at full load, which is more than most deep cycle batteries can supply without suffering damage. But even ignoring that issue, both the winch and the driving lights draw more current than can be supplied by the DC-DC charger. This means the winch will rapidly drain the battery, and the driving lights will not be operating at their optimum voltage.

The bottom line is that both these accessories will work far better if connected to the starting battery, which is supplied directly by the 200's 140-amp alternator, than from the auxiliary battery which is being supplied by the 25-amp DC-DC charger.

What about Lithium batteries? LiFePO4

Update July 2020
Lithium batteries (specifically LiFePO4) are becoming more popular in camping and caravanning applications due to falling costs, higher capacities and cycling advantages over traditional lead-acid batteries, including AGM and deep cycle versions. Lithium batteries can be discharged further without causing damage, and their voltage doesn't drop as they are discharged, unlike lead-acid batteries.

However, I remain skeptical about their long term durability in underbonnet applications, primarily due to the inherent temperature limitations with lithium battery technology. Most brands specify a maximum operating temperature of 80-85ºC. I have observed temperatures of around 90ºC in the vicinity of the battery. Apart from ambient temperatures, lithium batteries generate substantial internal heat when charging and discharging at high currents. Winches can draw 400A or more, which is beyond the capability of most (but not all) lithium batteries. Even those that can cope with such high loads usually have a very limited operating duration at that sort of current draw.

While I don’t doubt that they will last for some time underbonnet, I do believe their life would be limited if regularly operated at high temperatures, which makes their value for money questionable unless you really need some of their key advantages, such as lower weight or regular deep discharge capabilities. All that said, there are now a couple of brands that offer underbonnet lithium cranking batteries with a 2-year warranty.

At this time I wouldn’t personally install one underbonnet. However, the 120Ah LiFePO4 are an excellent choice for camper-trailers, caravans or a third battery for the rear of the LandCruiser. They can be charged direct from the alternator, or via a lithium-compatible DC-DC charger such as the REDARC BCDC1240D or BCDC1250D, which also manages solar input if required.


The "Installation" section should not be taken as instructions. It is simply a documenting of the procedure I followed for my own installation. No warranty is provided as to the accuracy of the information, and/or whether it applies in your situation or to your vehicle. If you're not qualified and/or don't have the correct equipment, have the dual batteries and charger fitted professionally.

  • There are potentially lethal dangers if incorrect wiring or installation procedures cause a fire.
  • There is the potential for expensive vehicle and accessory damage from improper installation.

If you undertake your own battery or charger installation, you do so entirely at your own risk.


Links below are eBay affiliate links. If you click on a link and make a purchase, I may be compensated by eBay. The price you pay is unaffected.

DC-DC Charger Installation

Click to Enlarge

Step 1: Remove the original batteries and parallel wiring

  • Remove the trim cover by pushing down on the centre of each retaining clip, then lifting the clips out.
  • Disconnect the negative/earth terminal clamp from each battery and secure the cables to prevent them touching the battery terminals.
  • Disconnect the positive terminal clamp from each battery
  • Disconnect the heavy cable joining the positive terminal clamp of each battery, and remove the cable. It won't be reused.
  • Remove the battery retaining clamps and remove each battery from the vehicle.
  • If you break/lose any of the clips, the correct ones are here on eBay.

Step 2: Wire the DC-DC charger

Cut and attach the following cables to wire the charger:

  • 8mm2 (8AWG) cable to run from the charger's RED wire to the starting battery (left side of the vehicle). Join to the charger with a heavy crimp & solder joiner. Crimp/solder one of the 6mm eye terminals included with the FK40 fuse kit to the other end.
  • 8mm2 (8AWG) cable to run from the charger's BROWN wire to the auxiliary battery (right side of the vehicle). Join to the charger with a heavy crimp & solder joiner. Crimp/solder one of the 6mm eye terminals included with the FK40 fuse kit to the other end.
  • Crimp & solder a heavy 6mm eye terminal to the charger's BLACK wire.
  • If you have solar panels, connect the YELLOW wire from the Redarc charger to the positive output from the panel(s). If you don't have solar panels, secure the yellow cable and tape the end of it. I'm attaching mine to a 50A Anderson plug for ease of future use. The other terminal on the Anderson plug connects to battery negative/chassis 'earth'. WARNING: Solar panels produce DC power even in shade and can cause electrocution. Cover panels from light and use extreme caution when wiring solar panels.
  • The BLUE, GREEN and ORANGE wires are not required for my installation, so I am cutting them off to slightly different lengths, then encasing them in heat-shrink tube. Check the Redarc manual to verify if you need to use these wires for your vehicle and/or auxiliary battery type.
  • Create two small loops of 8mm2 cable (around 100mm in length). On one end of each, crimp/solder one of the 6mm eye terminals included in the FK40 kit. On the other end of each, crimp/solder an 8mm eye terminal.
  • Cover all joins and terminal points with heat shrink tubing. 10mm is the size you'll need.
  • Cover all cables with split tubing. You'll need 7mm to run the single cables over to the batteries, and 10mm for multiple cables, such as for the solar anderson plug.

Step 3: Install the DC-DC charger

  • Install the charger into the REDARC bracket using the supplied 4x screws and nyloc nuts supplied.See photo for correct orientation.
  • Remove the factory bolt adjacent to the bonnet latch (10mm head), and the bolt retaining the horn (12mm head). See photo to identify the correct bolts.
  • Sit the charger on top of the radiator support panel, and run the cables over to the starting and auxiliary batteries.
  • Lower the charger down into the gap between the grille and radiator.
  • Using the M6x20mm bolt and washer supplied with the bracket, loosely attach the lower mounting point of the charger bracket to the captive nut in the vertical support.
  • Attach the top two mounting points using the two bolts removed earlier. Don't forget to reattach the horn! When all the bolts are loosely fitted, you can tighten all of them.
  • Connect the negative cable from the charger (and Anderson solar connector if fitted) to the battery or a good chassis ground point. If you connect it to the charger bracket using the lower mounting bolt, ensure that the bracket itself has a good connection to battery negative by running a cable from the bracket to the negative terminal on the battery or a chassis ground point.
  • Secure the cabling with cable ties to prevent chafing/shorts.

Step 4: Install the new batteries and complete the wiring

  • Place the new accessory/deep cycle battery on the right (driver) side of the vehicle.
  • Place the new starting battery on the left (passenger) side of the vehicle.
  • Fit and tighten the factory retaining brackets for each battery,
  • Attach the wires from the charger to one side of the each fuse holder, and run one of the small loops from the other side of each fuse holder to the positive terminals of each battery. Attach the rest of the positive battery connections.
  • Make all the negative battery terminal connections.
  • Start the vehicle and verify the operation of accessories and the Redarc DC-DC charger.

Step 5: Cut and refit the trim panel

  • Cut and attach the template supplied with the charger bracket to the trim panel.
  • Drill out two 12mm holes as shown on the template. I drilled two smaller pilot holes first.
  • Join the two holes to create the viewing window.
  • Refit the trim panel to the vehicle and secure with 7 factory clips.
  • If you break or lose any of the trim clips, you can find the correct ones here on eBay or here on Amazon.

Use the icons below to
share or like this page:


Scroll to Top