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Installing the Dual Battery System Part 1

Written by Kobus on July 12, 2011

Our 15+ month trip to Argentina will require some luxuries, like a fridge and the ability to charge our laptops and cameras. After months of research we decided to finally put dremel to plastic and steel and give Blue’s electrics a little make over.

What we used:

  • Optima Dual Battery Box from RuffStuff
  • Optima Yellow top 34/78, as auxiliary battery
  • Optima Red top 34/78, as starter battery
  • Overflow reservoir pipe, roughly a foot and a half
  • 1985 Toyota pickup truck overflow reservoir
  • 6 Teflon spacers to support the batteries
  • 1Teflon Cutting board as battery base
  • 4 x 8m 3.5inch Bolts, nuts and lock washers
  • 1 can of Spray paint engine enamel

Red top and Yellow top Optima Battery in RuffStuff box

Here are the two batteries in the tray. We later painted the bare metal with heat resistant black enamel paint to keep the rust off.

standard battery removed

This shows the modifications we would have to make to fit the dual battery tray in roughly the same position as the stock battery mount.

standard battery removed view 2

Side view with the stock battery removed and the radiator overflow reservoir still in place.

View of cut battery bracket

The first step was to remove the standard plastic battery plate and mount, and one leg of the fuse box mounting. The dremel made quick work of the battery bracket, and we drilled out the rivet that held the fuse box leg mount. After cutting the metal we painted over the exposed pieces to stop rust from setting in.

view of cut fan shroud

Next we removed the radiator overflow reservoir and cut the fan shroud. We left the edge of the shroud intact to avoid compromising the structure and mounting points.

We filled in the hole with a couple layers of duct tape, this was to avoid hot air flowing directly onto the batteries and to make sure the fan still works as intended.


We mounted the solenoid in the only accessible position, next to the firewall. The solenoid acts as the connection between the two batteries. It engages once the engine has been running for five minutes and the starter battery voltage is at a safe level. This is to ensure that the main starter battery is never drained by charging the auxiliary battery. We'd rather have a car that starts than a cold fridge!

Overflow bottle

The last major modification was to move radiator overflow reservoir. The only place it would fit is next to the air filter, on the opposite side of the engine bay from where it was initially mounted.

To make matters worse, the standard overflow reservoir would not fit, it was too long and would not sit low enough without making contact with the hood or hoses below. Luckily we were able to fit a reservoir taken from a 1985 Toyota Pickup. Not only is the bottle smaller, it has a convenient mounting bracket that made it simple to attach securely.

We ground down a piece of angle steel and attached it from one of the bolts holding the air filter box to the reservoir. As a last bit of insurance we wrapped the bottle in rubber to stop any wear as a result of rubbing against the fan shroud and air filter box.

mount battery box

To mount the battery box, we cut a teflon cutting board to fit under the box. This acted as a base for the battery tray and lifted the batteries enough that we could re-attach the fuse box to one of its original mounting points.

We drilled four holes through the box, teflon board and wheel well. We used teflon spacers in the gap between the wheel well and original battery tray to stop the mount from caving in as we tightened the bolts. After everything was in place we sprayed the bolts under the wheel well with enamel and called it a night.

In part 2 we'll cover the wiring of the batteries, solenoid, fridge and power inverter.

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