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Jun 11, 2023


AS THE days of pointing our old 4x4 toward the back country, provisioned only with an Esky and Coleman stove fade into our rear-view mirror, we find ourselves in a landscape of technology and

AS THE days of pointing our old 4x4 toward the back country, provisioned only with an Esky and Coleman stove fade into our rear-view mirror, we find ourselves in a landscape of technology and electronic gizmos.

We’ve added fridge-freezers, camp lighting, USB ports, and a host of accessories with an appetite for power. If you are mobile each day, a single battery will probably suffice. But if you set up camp for more than a night, adding an auxiliary battery might be on the horizon.

In this review we test the latest management systems, mounts, and batteries that won’t leave you in the middle of the outback with a slab of warm coldies.

The principle behind a management system is that it charges an auxiliary battery when power is available and disconnects, or ‘unlinks’, when voltage reaches a predetermined level to avoid killing your main cell. Options are full manual, voltage-sensitive relays (VSR) and programmed relays.

Regarding batteries, the most common are flooded lead-acid (wet), absorbent glass mat (AGM), and lithium iron phosphate (LiFePO4). The former two are available in standard or deep cycle. Deep cycles are generally used as auxiliaries, as conventional batteries can be damaged if fully discharged.

Lithium offers premium performance but at significant cost and should not be mounted in an engine compartment. Regardless of type, a battery needs proper care to maximise its lifespan.

Our install platforms were a 2015 JK and Gen III Toyota Tacoma, and we selected systems from National Luna, TJM’s Intelligent Battery Systems (IBS), Redarc, CTEK, and Blue Sea. Mounting trays are from Mountain Off-Road Enterprises and Off-Grid Engineering which offer turnkey systems.

When the nearest roadhouse is 200 kilometres away, you can’t cut corners under the bonnet when it comes to battery selection. For this review we sourced cells from Odyssey (Extreme Series) and Optima (Red Top and Yellow Top deep cycle). While a few management systems are nearly bolt-in, some require a more technical hand.

To evaluate each in a controlled environment, we set up a bench test. Current was supplied by an MCP DC power supply, and load was provided via a 2000-watt inverter powering an ARB fridge-freezer, AC battery charger set to 6amp output, and our photo studio lighting. Voltage and amperage, along with solar input, were recorded with a Powerwerx DC power analyser.

Each system was run for several hours to experience multiple charge/discharge cycles while we evaluated its attributes: link/unlink voltage, over and undercurrent cutoff, under/overcurrent alarms, etc. Goal Zero solar panels provided power to units that accommodated wind or solar, and proper function was confirmed.

Other considerations were manual-link options, single-battery function, IP ratings (moisture and contaminant intrusion), completeness of kit, available accessories, ease of operation, and quality of instructions.

Newer vehicles have variable-output alternators (VOA) which reduce voltage based on a variety of conditions to reduce parasitic drag on the engine. Two systems reviewed accommodate this technology.

Lastly, winches can draw significant amperage during heavy pulls, and a single battery and alternator will not keep up with demand. With the exception of one system, an old-school manual switch would be required to draw this level of current from both banks.

Without further ado, we present some of the best dual-battery systems on the market … we hope you get a charge out of them.

REDARC has 40 years of experience providing mobile electrical components for the Australian outback. The award-winning BCD1225D offers an array of advanced options including multi-phase charging algorithms and solar/wind input compatibility, and it plays well with VOAs. It is sold à la carte, so you’ll need to source cable, lugs, fuse kits and hardware. We added their remote in-cab dual-voltage gauge.

During installation we wired it for profile ‘A’, specific to AGM batteries. Each algorithm has a defined charge cycle (boost, absorption and float) to ensure maximum service from your batteries. A ‘test mode’ evaluates input/output levels and presence of an auxiliary battery, and error codes are identified via a series of LED lights.

The BCDC1225D features an MPPT regulator and leads for solar input, and their unique Green Power Priority directs that energy to the house battery before charging the main. It can be mounted in the engine bay or on the chassis, but should be kept away from high-heat sources, as its thermal protection kicks in at 79.5C.

Unfortunately, its 25amp capacity does not allow jumping a dead start battery and there is no manual link. We would suggest an auxiliary Perko-style switch to connect both batteries for winching or jumping the main.

Instructions are excellent but set-up is a bit technical, and if you have a VOA you will need to locate your ignition circuit. During testing the BDC1225D performed flawlessly; it kept both batteries healthy and Green Power Priority managed solar input as intended. When the dust settled, the Redarc headed home with our High-Tech Award.

AVAILABLE FROM: www.redarc.com.auRRP: $609.10 BCDC1225D; $196.15 gauge; $72.67 fuse kit.WE SAY: Editor’s High-Tech Award winner. Made in Australia, with a two-year warranty.

POSITIVEWater and dustproofMulti-stage chargingBuilt-in solar controllerVOA compatible

NEGATIVELow amperage ratingLacks manual linkCost

THE CTEK D250SE also lands in the high-tech category. It will service an auxiliary bank up to 300amp/h and all 12-volt battery types. There are separate charging algorithms for AGM and lithium cells, and selection is made during the installation of wiring.

It efficiently manages solar input via an internal MPPT regulator, and when the auxiliary bank is topped off power is directed to the primary battery. A unique feature of the D250SE is its thermal sensor, which signals the mother ship if temperatures reach damaging levels. It is IP65 rated for dust and water protection. The 20amp maximum does not accommodate a manual link for jump starting, but combined with CTEK’s Smartpass 120S capacity rises to 140amp.

Installation in our 2018 Tacoma was simple, and the instruction booklet is excellent. These units mount side-by-side, so you’ll need to confirm you have the real estate available. We opted for the 250SE and will add the Smartpass if needed.

In the lab, the 250SE worked as intended, directing current from our solar panels to the house bank, then the start battery. This is a well-thought-out system and was in the running for the High-Tech award, falling short only due to its operating temperature limitations.

AVAILABLE FROM: www.ctek.com/auRRP: $419 D250SE; $457.57 Smartpass 120S.WE SAY: A well-thought-out system. Made in China and comes with a two-year warranty.

POSITIVEWater and dustproofVOA compatibleBuilt-in solar controllerDedicated charging algorithms

NEGATIVELow maximum amperageLacks voltage meterLimited operating temperatureCost

IBS (Intelligent Battery Systems) was formed in 1996 after its founder Beat Wyss became stranded in Western Australia with a flat battery. Returning to Switzerland he developed the DBS, or Dual Battery System. This is a comprehensive kit, and includes all components needed for installation: solenoid, battery terminals, control panel, harness and cables.

This system allows for full control of functions, as well as monitoring battery voltages levels, from the driver’s seat. The bi-directional relay automatically closes the circuit when the main bank reaches 13.1 volts and opens at about 12.5 volts (as tested).

It allows single-battery operation via its ‘trailer recognition’ feature, has an audible over/under current alarm, and is compatible with all 12-volt cells – though it must be pre-programmed for LiFePO4s. Vehicles with VOAs will require their Mini ATO compensator or IBS’s new Dual Battery Manager.

Manual link-start is accessed from the control panel, and with a 200amp capacity (500amp surge) it will easily jump your main and assist with moderate winch loads. Mounting location should not be subjected to submersion, as this unit is not waterproof. On the bench, everything functioned as prescribed, installation was painless and instructions clear. This is a very functional product at an affordable price, and thus receives our Best Buy Award.

AVAILABLE FROM: ibs-tech.ch (also available from TJM outlets)RRP: US$517 IBS-DBS EM.WE SAY: Editor’s Best Buy Award winner. Made in Switzerland and carries a 1-year warranty.

POSITIVEComprehensive kitIn-cab control panelSimple installation

NEGATIVENot waterproofNot VOA compatibleLacks solar regulator

NATIONAL Luna (NL) originally developed power options for solar-powered vaccine refrigerators for remote regions of Africa. The application was perfect for the overland crowd and NL has become a household name. Similar to the IBS, it is a split charging system, all functions are monitored via a dash-mounted panel, and it does not accommodate variable output alternators. This is a comprehensive kit and includes everything needed for installation: terminals, lugs, fuses, hardware, harnesses and cables.

Shortly after startup the solenoid links both banks, and they stay linked until voltage drops below 12.7 volts, specifically after the engine is off and accessories are running. A dragstrip-style LED Christmas tree on the monitor keeps the user apprised of voltage levels and if there is a problem.

The ‘set’ and ‘on’ buttons perform several functions, including a timer override and manual linking. You can jump the main battery from the house unit if needed, but due to its 100amp fuse it is suggested you let charge levels equalize for a few minutes first. Also, if the auxiliary battery is removed the system will throw an error code unless you disconnect a ground wire.

Instructions are thorough and set-up was easy, but with an IP40 rating it should not be subjected to excessive water. Bench evaluation revealed flawless operation with the exception of the 11.4-volt failure alarm, which we did not test. This is a nice kit and was easily in the running for our Best Buy Award, but its 85amp continuous-operation limit (400amp surge) held it back.

AVAILABLE FROM: www.nationalluna.com.auRRP: US$403.WE SAY: Nice kit. Made in South Africa, with a 3-year warranty.

POSITIVEEasy installationComprehensive kitIn-cab monitor

NEGATIVELow amperage capacityLacks solar regulatorNot waterproofLacks VOA compatibility

WE first viewed Off-Grid’s dual-battery system at an off-road event and were immediately impressed with the beautiful CNC-milled aluminium mounting bracket. This comprehensive kit includes hardware, a plug-n-play braided harness, terminal ends, pre-cut cables, and Blue Sea ML-ACR isolator. Blue Sea, purveyors of battery management systems for the marine industry, has earned a stellar reputation and their products have made a natural crossover to overland applications.

The ML-ACR lacks fancy LED arrays, but it gets the job done with simplicity and rugged components. After starting the engine, the magnetic-latching relay links batteries when voltage reaches 13.5, then ‘unlatches’ if voltage drops to 12.75 for more than 30 seconds. If any battery exceeds 16.2 or drops below 9.6 volts, the system enters lockout mode to protect components.

Its 500amp capacity and manual link easily accommodate jump starting and extended winching operations. From the dash-mounted toggle you can manually link batteries, isolate banks or turn the system off, and a dial on the base unit allows you to latch or lockout the system. Its IP66 rating is best-in-class and it performed flawlessly in the lab.

Installing the mount required fabricating a riser plate, which we did, but they say their new design will be bolt-in.

The ML-ACR does not accommodate VOAs, so we substituted the Redarc on the Tacoma. But for non-VOA vehicles, the ML-ACR is one tough unit with the fortitude to take a beating. FYI, its new home will be on my ’82 Hilux.

AVAILABLE FROM: www.enerdrive.com.auRRP: $430 Mount & ML-ACR.WE SAY: Built to cop it. Made in USA (mount) and Mexico (ML-ACR) with a lifetime warranty.

POSITIVEBest-in-class waterproof ratingBest-in-class amperage ratingLifetime warrantyHigh-quality construction

NEGATIVELacks solar regulatorLacks voltage meterNot VOA compatibleMount required fab work

IF you only need a dual-battery tray, Mountain Off-Road offers a high-quality option for 2007-and-up Jeep JKs. Crafted from powder-coated 1/8-inch plate steel, it incorporates the OE attachment points and accommodates two Group 34 batteries.

AVAILABLE FROM: https://mountainoffroad.comRRP: US$154WE SAY: High-quality tray for 2007+ Jeep JKs and made in USA.