Frequently Asked Questions


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 good way to accomplish this.  All of this can be prevented by adding a second "dual purpose", high quality AGM 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 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:  Our “side-by-side” battery systems were specifically designed to use Group 35 AGM batteries.  While any high-quality Group 35 AGM battery will work, we recommend the the Odyssey PC1400 Group 35, Northstar Battery Group 35 or Full Throttle Battery Group 35.

For the “split systems”, the same brand recommendations apply.  See below for the specific sizes needed for each system.


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

Early model FJ Cruiser (07-09):  Group 35 fits perfect.  Group 34 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 and it actually works quite well.

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:  Sure, with a certain understanding.  Ask any expert and they’ll tell you: It is recommended that all batteries in a “bank” or battery system be of the same size, age, and construction type.  This has to do with the difference in charging rates amongst battery types and sizes.  With different batteries in the same bank, one of them is bound to be over or under charged, thus drastically reducing its life.  In a perfect situation, one would purchase two brand new, identical batteries for a dual battery system.

Q:  But, I really don’t want to buy two new batteries.  Are you sure I can’t get away with running different batteries? Pretty please?

A:  Sure. Plenty of people do it and get away with it.  If you’re going to do it, the most important rule to abide by is making sure the construction type of the batteries is the same.  If your old battery is a traditional flooded cell, then make sure your second battery is the same.  If your old battery is an AGM, then make sure your new battery is the same.  The second most important is size.  Try and match them up as close as possible.


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.

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.