The UK build of the 80-series Land Cruiser comes with dual batteries to create a 24v system for starting in cold environments. Basically the starter system ties the two batteries together to run the 24v starter solenoid, then it separates the two and runs the accessories off of one battery at 12v. We decided to keep the 24v starting system and to add an additional 12v battery. We chose the Optima yellow top batteries as they allow for deep cycle application (which means that they can be discharged and recharged many times) as well as a high output of cold cranking amps (needed to start the vehicle). These batteries are also sealed gel so they can be mounted in any configuration and won’t spill. They are also shock and vibration resistant, and can be discharged to a lower voltage than other batteries and still be recharged without performance issues. We replaced the two original batteries with the Optima and then added a third yellow top which was mounted behind the right rear passenger seat. This third battery is tied into the vehicles charging system through a fuse panel and the IBS dual battery systems 200A relay. The IBS dual battery monitor allows me to see the charge level and voltage of the auxiliary battery. This system, basically, works by monitoring the voltage of the starter batteries (under the hood). Once it determines they are fully charged it connects the third battery through the relay which begins it in its charge cycle. When I am starting the vehicle the third battery is disconnected from the system unless, in the case of a dead starter battery, I need it and press the override switch which connects all three batteries for 30 minutes. The LED lights from ELS, the ARB Fridge/Freezer, and the winch are connected to the third battery.
UPDATE: The Optima batteries have been exactly what we need. They were completely depleted during the shipping process and I was able to roll-start the truck and recharge both batteries and the auxiliary battery with only the alternator. I purchased a CTEK MXS 5.0 battery charger which I ran to the auxiliary batteries in the rear. I removed it and connected it to each battery individually and reconditioned them. The batteries work better than when I purchased them new. I reconnected the CTEK charger to the auxiliary battery. i use it when we stay at campsites that have power hookups.
I also purchased two 90-watt solar panels from Set Solar in Cape Town. The panels are made by set Solar and were half the cost of any I could find in hardware stores. I used their cables, connectors and charge controller and connected them the distribution panel which runs to the auxiliary battery. I had Lowveld Canvas in Nelspruit make a case for them so I could carry them on the roof rack. We spent 5 days at Beverlack (north of Cape Town) over the New Year. It was very hot and I ran the fridge for the entire time and only hooked the solar up during the day. The panels kept the batteries charged without any trouble. I am pleased with the solar setup we have, the battery charger, and the dual battery setup from IBS. My auxiliary is a 55 AH battery and in the future I may upgrade it to a slightly larger version.