Dual battery system

Hi Glyn,

ARB's arrangement sounds fine to me. Keeping the auxilliary battery (presumably an AGM deep-cycle) out of the heat of the engine bay is good sense for battery life.

Posted from along the track near Marble Bar.

If it is a solenoid isolator system which you control OR it is a VSR type which switches on automatically, you shouldn't need a battery charger at all.
The vehicles alternator will deliver 14. 3v or14.4v to the battery and with appropriate sized cable supplying the battery, it will then become charged.
I have an in tub battery (AGM full River) and also one in the Tvan linked with an anderson cable. All batteries get charged.

Manual isolator/relay supplies main to the aux batteries. All has worked that way for more than 5 years. Original 2 x AGM batteries.

Batteries are heavy, I would not be putting them behind the back axle. I would try and place between the two axles if possible which gives for a more balanced vehicle.

What are your plans for the rear tub ? If you plan on a canopy and drawers, then there is plenty of room in the side wings of the drawers for the second battery. Of course if you want to keep the tub open, that's a different matter - just another option to consider.

John

Heavy leads might have been the way to go in the past but now most modern vehicles control the alternator voltage after a short period of running and lower the alternator output to around 13.2 volts which would never fully charge a battery even it this voltage was applied directly to the battery, ie. no voltage drop in the connecting leads.
There are a number of options available such as the diode/fuse booster or the best of all, a DC/DC charger. Unless you run extremely heavy wires the distance it is to the proposed battery location and stop the alternate voltage dropping you will never get the battery to full charge. In my view the DC/DC charger is the best option but bear in mind they are not cheap.
The maths [well Ohm's Law] tells the story. If your leads have a total resistance of 0.05 ohms [remember there are 2 wires and associated connections in the circuit] and the charge current is say 20 amps, there would be 1 volt dropped across the cables. If the voltage from the alternator was 14.4 volts [best case] you would have only 13.4 v at the battery.
I'd go with the ARB solution.
Ken