Dual battery set up

Hi all,
Im more or less a total newbie to all things 4x4, ive been researching as much as possible and have found tonnes of great stuff on here. When i search 'Dual battery' setups, there are millions of hits and i dont know where to begin. Ive been reading that newer vehicles often use a variable voltage alternator to keep emissions/fuel consumption lower. This apparently means that i cant simply use an isolator/diode to split my batteries. Lots of people talk about using a dc-dc charger set up to get full charges to both batteries. Fair enough, but couldnt i just set up my batteries in parallel and my ute alternator would just see it as a really big battery and just charge it up almost as it normally does? Couldnt i then just have an electrical diode to restrict the battery flow one way, so the main battery is for cranking and the second then is hooked up to fridge etc? This would mean that the fridge could never draw elec from the cranking battery, right? When i research and find Aus sites its all dc-dc/bcdc etc, but in US they seem just to put them in parallel. Similar in UK, no one even seems to have heard of the dc-dc charger system to set up dual batteries? They just connect batteries via the towbar cable into a camper/caravan.

Any thoughts? I have a Ranger 2017 and i am trying to find a simple, yet definitive way to do this, wiring and all.
The problem with wiring them in parallel is that you are essentially making 1 big battery. This means that if you are at camp and running your fridge, some lights etc. and you drain your battery to far then you can't start your vehicle. If they are isolated your starting battery is still good to go. Also with parallel you have to be careful to use the same chemistry.


Well-Known Member
A DC-DC charger boosts the charge when the variable voltage alternator reduces its output AND/OR when the cabling in your 12 volt installation is inadequate. If the charge is not boosted, your auxillary battery will never reach full charge.


Well-Known Member
I'm no expert but if your alternator is capable of charging your starter battery to full then why would it not charge an aux battery the same through a basic dual battery isolator that protects the starter battery when the motor is off something like the baintech 100amp kit etc. I'm not trying to offer bad advice but if you put a voltmeter on the aux battery as a permanent gauge then you will soon know if it can do the job by seeing how many volts the battery is charged to also you may have to fit an alternator booster diode to help which I see some people do. With the voltmeter gauge fitted in line you can monitor the battery so your fridge, accessories don't drop the voltage below the recommended level. I'm sure there are lots of people who still charge their aux battery without using chargers in modern vehicles without any problems if their mounted in the vehicle. It may be different if their in a camper or van others will know what might be best but keeping it simple and not have to spend unnecessary money on something you really don't need is the way to go.
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4x4 Earth Contributer
I have a second battery in back of my Troopy. It is a deep cycle in an Ark Pack and connected to my main starter battery by an anderson plug. It receives charge from main battery every second day I drive around town and on a trip most days. When camping I disconnect the main battery and connect a solar panel with anderson plug. I have a red arc isolator on the main starting battery which protects it when ignition is switched off.
I run a sixty five litre evakool travelmate at around 2 to 3 degrees and carry my drinks, vegies, milk, butter, cheese, etc. etc. and it works good.
I do not run anything else on it and I have had it for a few years now. Sometimes I do a 240 cycle charge at home or in caravan parks to top it up.


Well-Known Member
I could sell you my BCDC Redarc charger for around $300 I bought it early last yr I think it's to big for my old GQ patrols alternator I am looking at going to a 25amp one.


Active Member