Dual / Back-up Battery Installation

Back-up battery in Mk III Range Rover

Classic Range Rover Installations
P38 Installations
Mark III Range Rover Installations

Photo: Ray Lindner's back-up battery installation on his Mk III Range Rover.

A second battery is useful not only for emergency starting if the main battery goes bad out in the backwoods, but also for winching operations so as to avoid draining the starting battery. Various owners have reported methods of installing a second battery in each of the various Range Rover models, and their experiences are reported below.

Classic Range Rover

The Classic models have a spare battery space on the left front corner under the air intake horn, making installation relatively easy. For details, see Ron Beckett's installation on his Classic, and the well-illustrated installation done by John Purnell.

P38 Models
Rear second battery instal by Jim HaverWhen changing the battery on my P38 model, I have noticed the battery tray in the P38 is very wide. I have always replaced my battery with the OEM Interstate model which perfectly fits the space, but when investigating various other brands of battery that would be suitable I have found they are considerably smaller. Therefore, I think it might be possible to fit two modern smaller batteries in side by side.

Wayne Hubbell reports that on his 1999 4.6, there is room for a second battery right behind the main battery. The space is small, but the new "Black Panther" batteries will easily fit. These are true deep cycle cells, of dry electrolyte design, that are extremely small for their capacity and current density. They are moderately expensive (around $200), but have a long life. He plans to fabricate a simple tray for it. He previously had a second battery with an isolator in his Jeep, but for this installation decided to go with a simpler high current solenoid system from Northwest Power Products.

Jim Haver did a very neat second battery installation in the spare tire compartment in the rear of his P38 Range Rover (photo at right), and posted a detailed illustrated description at this link. Note that in this case the intention was merely to power accessories when the engine is off, not to provide enough amps for starting. Jim was therefore able to tap into the wiring harness at the rear instead of running heavy cables as would be required in the latter case.

Mark III Range Rover
The Range Rover III comes with a convenient storage compartment under the loadspace floor behind the right hand rear wheel well. If you lift up the hinged floor pane and lift out the black plastic compartment liner/tray, you will see a fairly large empty space including threaded mounting holes for securing a small sealed battery, which can be dropped straight in. Wiring is also made easy as there is a thick battery cable running to the air suspension control computer, mounted just above the storage compartment.

Ray Lindner of Australia reports: "I installed a GELL Battery in the rear of the vehicle (see photos below). I use it to run a 12 volt fridge. A battery management system cuts out the main battery at a pre-set voltage when the vehicle is not running, thus ensuring the main battery will always start the car. I can camp for a couple of days and leave the fridge running all the time.  The main battery fully charges before the system re-charges the 2nd battery.

2nd battery

2nd battery hidden

"The Mark III Range Rover has a convenient storage bin at the Right Hand Rear of the luggage area. We fitted the battery into that space.  At the top of the two photos above, you will see a double 12 volt outlet.  The left hand photo shows the battery with the floor cover open and the other with it closed.  Apart from the dual outlet,  one would not know the second battery existed!

Tim Sanderson in Australia has some more hints to add after doing a similar but more elaborate installation on his 2003 DSE. He designs and sells dual battery charge controllers and associated equipment for a living, so his approach ensures that the two batteries will work together optimally. "When you open and remove the floor cover, there is a plastic storage bin. Just pull the long sides of the plastic bin in towards the centre of the bin and it will lift out. In the walls of the recess where the bin fits, there are battery mounting points already installed. If you are going to run nothing more than a small fridge then the wiring is also made easy as there is a thick battery cable running to the air suspension control computer, mounted just above the storage compartment. In the middle of the picture below, you can see a thick red cable winds down around to a bolt connection. You can pick up your positive for the auxiliary battery at this point and just find a solid earth to bolt your auxiliary battery’s negative to.

Dual battery controller

As I am also powering a camper trailer, I had to run separate twin sheathed 10mm battery cable from the main battery, down the left side of the RR and then across the rear to the dual battery controller (actually a triple battery controller) mounted in the rear battery compartment. From the dual battery controller, one cable goes to the auxiliary battery in the rear of the RR and another cable goes to an Anderson Plug to supply power to the trailer. Running new cable is a big job. It took 7 hours and required removing 27 panels and covers and the front seat!"




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Page revised February 1, 2012