12V/12v. Chargers

good DC DC chargers do an excellent job. Depends on your needs and requirements. How you use your batteries. To charge and use 2 auxilliary batteries correctly would require 2 DC DC chargers or a manual switch to switch between 2 batteries.

Hi Bob

I too have a patrol and the same battery configuration as you wish to have.

I won't go into the dc/dc charging side of things but on my 4.2 the start battery was on the drivers side whilst the aux battery was mounted on the passenger side.

Now as the start battery is a wet type and I wanted an agm as auxillary the heat from the turbo and exhaust was 300mm from the auxilly battery.
Apparently agm batteries don't take the heat as well as a wet battery.

Solution. For me I changed the batteries around so the wet start battery is now on the passenger side and the auxillary on the drivers side. With the auxillary further forward in position under the bonnet. I can mount a charger on or before the front radiator support, which would be the coolest area, whilst still being less than 250mm from the battery.

My patrol also has a battery surround with a air feed going through the inner guard which I used with the agm battery.

Hope this helps

Cheers Teza

With the current model Prados and Hiluxes there alternators are designed such as to not work to their full capacity constantly and will only charge your second battery to 80% regardless of the voltage drop issue for long cable runs.
The Dc/DC charger rectifies this issue.
I do not know how many other modern vehicles this effects and I am only a novice in this field but Member Olcoolone gave a detailed explanation of the workings of the modern alternators on the Hilux forum.
I have one fitted to my vehicle to increase my capacity and up the voltage for my second AGM battery

Bob,

In the situation you have just descibed, I don't believe you need a dc-dc charger.
The Thumper should have coume with it's own 30-40 amp charging kit and includes both a suitable sized heavy duty twin cable and a built-in isolator.

You will need a suitable charging circuit for your 120Ah which I assume is an AGM style.
My recommendation would be to purchase an ABR Sidewinder Flyer to contain your AGM battery. This unit also includes it's own charging cables, connectors, etc. and a really heavy duty twin cable.
By utilising the Flyer (which also has a built-in isolator) you would not need a separate charging circuit for the Thumper. The Flyer includes both input and output Anderson connectors, and you would only need to have a short patch lead to connect the Thumper to the output on the Flyer, thus joining the two battery packs in parallel.

I use a similar setup in my rig, although I have the two charging circuits mentioned above, one for the 75Ah Thumper (because I installed this first) and a second circuit for the Flyer. (contains a 100Ah AGM)
When I connect my camper trailer up, I plug into the output of the Flyer and have a dc-dc charger at the other end, (inside the camper) because of the extra long run.
This ensures the two 80Ah batteries in the camper get a full and efficient charge.

I don't always take the thumper now, but include it when camping in the tent and also when travelling to remote destinations where the jump start capability of the Thumper provides an extra emergency facility.

The Flyer kit will cost around $375 which is close to the cost of a dc-dc battery charger but it will give a more flexible solution. You really need to secure your large AGM battery in the back of your vehicle and need an isolator in the circuit to protect your starting battery.
You shouldn't need a dc-dc charger when both batteries are in the back of your rig as the cable run (I think Dereck provides 6 B&S cable) is plenty big enough.

Hope this information assists you with the ability to choose a cost effective solution.
If you contact Derek Bester at Sidewinder he would be only too happy to assist you.