Q:  Why would I want/ need a dual battery system?

A:  As we add accessories to our vehicle, such as auxiliary lighting, air compressors, and mobile refrigerators, the factory electrical system can become overloaded quickly. Most gas powered vehicles come with a single "starting" style battery which are not designed to be drained and recharged multiple times.  Doing this will drastically shorten its life and inevitably leave you stranded when you need it the most.  Running accessories with the vehicle off (such as your camp lights or fridge) is a quick way to accomplish this.  All of this can be prevented by adding a second "dual purpose", high quality battery.  This second, or "auxiliary" battery is dedicated to running your accessories so the starting battery can be left alone to do its job.

Adding a second battery to your vehicle also adds a level of redundancy and safety when traveling in remote areas.  Whether its a simple day trip in to the hills or a trek across international borders, a dead battery can ruin a good trip.  With an Off-Grid Engineering dual battery system, the batteries can be combined in the event of a dead starting battery to "self jump-start" your vehicle and get you home safely.


Q: How does a dual battery system work?

A:  A standard automotive “dual battery system” is nothing more than an additional battery installed in the vehicle intended to run auxiliary accessories.  This battery is simply wired “in parallel” to the main battery so that it charges and discharges at the same time.  A properly designed system will incorporate a relay that interrupts the parallel circuit when there is no charging source present (such as the alternator, when the vehicle is running).  Most modern systems have "smart relays" that can automatically detect when the vehicle is running or not.

Simply put, a proper system will ensure that both batteries charge when the vehicle is running and are totally isolated from each other when the vehicle is not.  When the batteries are “isolated”, they operate independently and cannot affect one another.  This means that one would be free to drain the auxiliary battery without fear of draining the starting battery and being stranded.


Q: What is the difference between the Redarc BCDC and the Blue-Sea ML-ACR?

A: The Blue Sea Systems ML-ACR is a “smart relay”. It physically links the batteries together in parallel, so that they can charge together when the vehicle is running.

ML-ACR Pros:

  • Can recognize a charging source from either side and share that charging source with the other battery.
  • Handles up to 500-amp continuous current flow in both directions.
  • Manual override features for self-jump start or other high amp draw scenarios, provides ultimate control over battery system behavior.

ML-ACR Cons (when compared to the Redarc):

  • Requires the use of two similar batteries.
  • Is not a battery charger. Meaning, it does nothing to alter the current to charge the battery it is linked to. It simply passes current.
  • Does not have any other features, such as a built-in solar charge controller.

The Redarc BCDC 1225D is a DC-to-DC battery charger. It takes a small amount of power from the alternator/ starting battery and sends the proper current to the auxiliary battery.

Redarc Pros:

  • Does not require matching batteries.
  • True in-vehicle battery charger. Will effectively charge auxiliary battery to 100%
  • Built-in solar charge controller. Simply add an unregulated solar panel.

Redarc Cons (when compared to the ML-ACR):

  • Single direction. Charges the auxiliary battery bank only.
  • Cannot link batteries together without additional hardware.
  • No manual control

As you can see, both methods of dual battery management have their merits. The Redarc is an excellent choice for those that want a “turn-key”, no-hassle, dual battery setup that will always maintain an appropriate charge on the secondary battery. The ML-ACR might appeal more to the heavy-duty user that frequently needs to combine battery banks or simply wants more manual control.

Q: Can I swap out the BCDC1225D for a BCDC1240D or BCDC1250D?

A: Unfortunately, no. The BCDC1225D is the correct choice for this application from the calculations we have done. The 40A will exceed the recommended nominal and maximum charging rate of AGM batteries of the size and capacity that can fit in the auxiliary location. Overcharging can result in excessive heat being produced, decreased battery lifespan, and decreased efficiency. The 40A can start to be considered for batteries of 115Ah or more, and REDARC recommends using 40A for battery banks of 200Ah and greater.

Q:  What makes Off-Grid Engineering dual battery systems the best choice for my vehicle?

A:  Many reasons!

  • Carefully thought-out designs:  Off-Grid Engineering battery trays and complete dual battery systems were each thoughtfully engineered for your specific vehicle!  We pride ourselves in providing a 100% complete kits.  No surprises or trips to the hardware store on installation day.  Our cables are cut and properly terminated to the exact length you’ll need for professional grade installation. High amperage fuses are provided for the necessary locations (something no other manufacturer provides!) Most of our kits are 100% bolt-in.  Detailed instructions come with every product.
  • Quality components:  All of our battery trays and tiedowns are designed, cut, machined, and hand-built in Colorado, USA. All of our complete dual battery systems are designed and built in the USA using as many American made components as we could possibly source. From the Blue Sea Systems relays and fuses, to the high strand count, ultra flexible battery cable, all the way down to brand-name 3M heat shrink, we refuse to cut corners on a single piece of our kits. There is simply no higher quality dual battery system available.
  • Small business values and integrity:  Off-Grid Engineering, LLC consists of 1-3 people, depending on work load (a true small business).  Chances are, if you have one of our products, it was built by yours truly.  We take our quality seriously and we stand behind every product that we send out the door.  If you ever have a problem with an Off-Grid Engineering product, we will do everything in our power to make it right.  Thats our promise to you.


 Q:  Which batteries do you recommend for your systems?

A:  Each product listing has it's own recommendation for batteries.


Q:  What is the largest battery I can fit in the passenger side trays?

A:  Most OGE trays so far have been designed to hold a Group 35 AGM battery perfectly.  With that being said, larger batteries can be fit in certain applications.  Here is what we have found so far:

2nd and 3rd Gen Tacomas: A Group 35 fits perfectly and is recommended. A Group 34 will fit if you’re willing to “massage” your AC lines out of the way but its hardly worth it for an average 3 Ah gain.  

4th Gen 4Runner:  MUST use Group 34R (Odyssey PC1500 Group 34R is our recommendation here, because Full Throttle does not make this size)

Early model FJ Cruiser (07-09):  Group 35 fits perfect.  Group 34R fits fine but tiedown will not be centered.

5th gen 4Runner and late model FJ Cruiser:  Group 35 fits perfectly.  Group 34 fits but tiedown will not be centered.  Group 24F is the largest battery that can be fit but is not generally recommended due to weight concerns.

Lexus GX470: Group 35 is the best fit we've found so far.  Anything wider or taller will not fit.

Q:  What is the largest battery that will fit in the driver’s side trays?

A:  Whatever the largest stock battery you can fit is.  Anything larger than a Group 35 will hang off the edges, but will remain plenty secure. Tacomas can fit Group 31 batteries.  Most other Toyota trucks and SUVS will be limited to a Group 24F or Group 27F


Q:  Can I keep my current battery and add another for a dual battery setup? I just bought a new battery or; I have a new truck and don’t want to replace the battery yet. 

A:  With our complete dual battery systems featuring the Redarc in-vehicle battery chargers, you can keep your factory battery and install an AGM, Gel, or Flooded battery as your auxiliary battery.  We do not recommend Lithium batteries for installation under the hood.

If you are using the Side-by-Side system with the Blue Sea Systems ML-ACR, then we heavily recommend that both batteries be of identical construction type. Meaning, both batteries need to be AGM, Gel, or Flooded.  This is because both batteries will be linked together while charging and they need to have similar charging characteristics.


Q:  I want to install a Group 31 in the factory position in my Tacoma or a larger battery in the factory position of my Toyota Truck.  Do I need a new battery tray?

A: No. Taller J-Hooks and a sturdier tiedown is all that is necessary.  Most aftermarket battery trays that advertise themselves as Group 31 battery trays do not offer any additional support to the sheet metal.  Check out the OGE machined aluminum tiedown to accomplish the same thing for a lot less money.


Q: Are your lead times accurate?

A: Our lead-times are kept up to date, but there are times when things may take a little bit longer as the full kits are built to order.


Q:  Do you offer installs?

A: No, we do not offer installs at this time. BVO Adventure Vehicles is our preferred choice for installers.


Q: Do you offer local pickup?

A: No we do not offer local pickup at this time. All orders will ship via UPS.

Off-Grid Engineering LLC is a limited liability company. Our products are designed for off-road use only and have not been tested for collision scenarios. We can not be held liable for faulty installation of products or damage to vehicles caused by the faulty use or damage of our products. Please do not modify any of our wiring or cable kits. We always recommend circuit protection/ fusible links for aftermarket wiring.