Setting up a dual battery system in your Toyota Hilux (2005 and on)

Author: Rod Webster   Date Posted:19 May 2017 

There are many tricks and traps when it comes to setting up a reliable auxiliary battery system in a Toyota Hilux so I've put this article together to help guide you when setting up your system. There will be many that disagree with some of my advice here but let you make an informed decision that is based on real world experience out there enjoying this marvelous country of ours.

Which Battery tray?

Well that's pretty easy. Just grab one of the ones sold right here on VMN. We live and breathe Hilux around here and we only list products on our online store that pass our stringent quality guidelines. We have used quite a bit of Outback Accessories gear over the years on our own Hilux and I have to say their gear has  stood up to the test of time so that's why we sell their product.

Which Battery?

Well to start with you need a N70Z sized battery. What type depends on your individual needs. One thing that you can be sure, your battery will get a pretty hard life keeping your fridge cold. One type we don't recommend is the AGM deep cycle battery for a few reasons:

  • They are simply too heavy to mount in a battery compartment regardless of the battery tray you choose. Early 2005 or so Hiluxes had a problem with cracked mud guards that was often traced back to fitment of an AGM battery. I believe that Toyota modified the design somewhere to toughen up the mudguard
  • The environment in the engine bay is not good for them due to heat (which they don't like) and also vibrations which can cause premature failure.

If you are not running a winch, then consider using a lead acid style deep cycle battery but if you are going to fit a winch, I recommend an all rounder style battery that copes with the rigors of winching yet also gives reasonable deep cycle performance and can be moved to your cranking battery if required.

Which charging system/Isolator?

The most important feature any charging system must do is to isolate the cranking battery once the engine is turned off so it never gets run down while stationary and leave you stranded in the morning. The isolator does this by monitoring the input voltage and when the voltage falls below a specific voltage, it flicks a relay switch that isolates the cranking battery from your auxiliary electrical system. When does the voltage fall below the threshold? Well it is below that threshold when the engine is off and rises above that threshold when the engine is started AND the cranking battery is fully charged. At this point the voltage rises as the alternator thinks it has done its job. This usually happens fairly quickly but can take a bit of time if the battery has  been run down a bit.

So battery charging systems fall into 2 broad groups and in my view many of them have been designed with overkill in mind to empty your wallet much more than is really necessary. Remember, when offroad, simple is good as it's easier to repair of find spare parts for. These are:

  • Simple battery isolators such as our Matson battery Isolator that allow the maximum alternator current pass through to charge your dual battery system. The factory alternator outputs 70 amps but my aftermarket Bosch alternator outputs 100 amps.
  • DC-DC chargers that do all sorts of smart stuff when charging your batteries but are limited to a fairly low charging current (eg the popular Redarc BCDC1220 only puts out 20 amps). Some even allow you to connect a solar panel to your charging system.

So ask yourself the question now. Why limit the ability of the charging system to charge your batteries? Why would I want to  charge at 20 amps and drive say 5 hours to charge my batteries when I can get the job done with an isolator and a 100 amp alternator in just one hour's driving?

Well the reason is that about the time the Hilux Vigo/N70 came on the market back in 2005, the car industry came under pressure to reduce energy consumption to meet emissions and fuel economy targets. One trick they played was to get the ECU to reduce the alternator output voltage after a period of time from the 13.8 volts used for years down to 13.2 volts. 13.8 volts is a perfect charging voltage for lead acid batteries but 13.2 volts is not so good.

So spurred on by the example of the amazing mains powered  Ctek multi stage battery chargers and some other wannabe brands, the technology was transferred to automotive applications and the DC-DC charger was born. Back in 2008  when I set up my Hilux, these did not even exist as I am sure if they did, ARB would have done their best to upsell me from the crappy Surepower isolator they stitched me up with.

In my view, the best system is the simplest and cheapest option and it works perfectly with my aftermarket alternator as it always seems to output 13.8 volts so an isolator works perfectly. I'm not sure if its the alternator or the auto sparky who fitted it for me that tricks the ECU into letting the alternator output 13.8 volts, but it works well for me.

Yeh, I know, you only have the standard Toyota Hilux alternator so it's going to reduce the voltage. Let me tell you about a really cool little trick that will let you charge your Toyota Hilux battery at 13.8 volts all day every day with a cheap as chips isolator and a cool little gadget that will only cost you $50 instead of $500 for a DC-DC charger. Just head over to ebay.com.au and search for alternator voltage booster  and choose the listing for your Hilux from a seller called hkbelect  who is a qualified auto sparky, don't grab  one of the cheap and nasty imported ones. This is a cleverly modified fuse that you pop into your fuse box on the alternator voltage sensing circuit that contains a diode. Now a diode induces a voltage drop of 0.6 volts across it so the ECU now senses a voltage of 13.2 volts when the alternator is happily pumping out 13.8 volts. This is well below the design limits of the Toyota electrics so it does no damage to your vehicle at all.

But won't my battery get overcharged?

No, not at all. A lead acid battery will only ever accept the current it need to become fully charged. You can add 47 different chargers to a battery system and the battery will just politely take what it needs and stop drinking up the current. 

But I want to use a solar panel as well

Well, that's absolutely fine. You don't need a fancy Ctek charger to do this as part of your engine battery charging  system. It is far easier and a hell of a lot cheaper to just add a dedicated MPPT solar charger and wire it in as a separate charging system. The one to get is a Tracer which you can find on eBay. There is another brand that has taken over this slot so I will update this when my electronic guru gets back from the Kimberleys in a few weeks. Lucky Sod!

But tow a caravan or camper trailer with solar panels on the roof

Even better, Just hook your auxiliary batteries into your isolator controlled dual batteries via an Anderson plug and let your caravan charging system also charge your vehicle batteries. Of course if you plug your van into mains power, an anderson plug extension lead is the perfect addition to keep your car battery  fully charged and let you park in a more convenient location. You can't do this with a DC-DC charger as the DC-DC charger prevents the charge from going back to the vehicle so the so called experts will want to sting you for a DC-DC charger in your trailer as well. 

So I had 2 Aux batteries in my Hilux and another 2 in my caravan and all of this worked perfectly driving down the road with 30 amps of solar on the van and 100 amps of alternator topping up 4 auxiliary batteries. I never needed to add the 3rd battery that there was provision for in the caravan.

But I have an absorption fridge in my van that draws 15 amps all the time

It might be unconventional but the best solution is to add a second  isolator to your auxiliary battery system and direct connect  it via a different colour anderson plug using heavy wire to your absorbtion fridge. I used a red Anderson plug for the fridge and a grey one to charge the batteries in the van. Different colour anderson plugs are not interchangeable so you can never get them mixed up. So how does this work? Well, you start your car, the cranking battery gets charged and the first isolator starts to charge you car batteries. After a while they are charged and the second isolator kicks in and starts to run your fridge. You will never have fridge problems again in you van. Well I never did anyway. The Matson isolator is ideal for this as it terminals are well protected to prevent any shorts occurring.

In conclusion

So if you follow the ideas I have outlaid in this article and correctly size the wires to your Aux batteries and camper trailer you will end up with a kick ass charging system and a few hundred dollars left in your pocket.. Hell, you might even plug a slow cooker into an inverter and cook dinner while driving down the road like one of my mates does! Believe me, this stuff works. Don't forget to buy your Hilux battery tray and Matson isolator from the VMN store.

e many tricks and traps when it comes to setting up a reliable auxiliary battery system in a Toyota Hilux so I've put this article together to help guide you when setting up your system. There will be many that disagree with some of my advice here but let you make an informed decision that is based on real world experience out there enjoying this marvelous country of ours.

 

Which Battery tray?

Well that's pretty easy. Just grab one of the ones sold right here on VMN. We live and breathe Hilux around here and we only list products on our online store that pass our stringent quality guidelines. We have used quite a bit of Outback Accessories gear over the years on our own Hilux and I have to say their gear has  stood up to the test of time so that's why we sell their product.

Which Battery?

Well to start with you need a N70Z sized battery. What type depends on your individual needs. One thing that you can be sure, your battery will get a pretty hard life keeping your fridge cold. One type we don't recommend is the AGM deep cycle battery for a few reasons:

  • They are simply too heavy to mount in a battery compartment regardless of the battery tray you choose. Early 2005 or so Hiluxes had a problem with cracked mud guards that was often traced back to fitment of an AGM battery. I believe that Toyota modified the design somewhere to toughen up the mudguard
  • The environment in the engine bay is not good for them due to heat (which they don't like) and also vibrations which can cause premature failure.

If you are not running a winch, then consider using a lead acid style deep cycle battery but if you are going to fit a winch, I recommend an all rounder style battery that copes with the rigors of winching yet also gives reasonable deep cycle performance and can be moved to your cranking battery if required.

Which charging system/Isolator?

The most important feature any charging system must do is to isolate the cranking battery once the engine is turned off so it never gets run down while stationary and leave you stranded in the morning. The isolator does this by monitoring the input voltage and when the voltage falls below a specific voltage, it flicks a relay switch that isolates the cranking battery from your auxiliary electrical system. When does the voltage fall below the threshold? Well it is below that threshold when the engine is off and rises above that threshold when the engine is started AND the cranking battery is fully charged. At this point the voltage rises as the alternator thinks it has done its job. This usually happens fairly quickly but can take a bit of time if the battery has  been run down a bit.

So battery charging systems fall into 2 broad groups and in my view many of them have been designed with overkill in mind to empty your wallet much more than is really necessary. Remember, when offroad, simple is good as it's easier to repair of find spare parts for. These are:

  • Simple battery isolators such as our Matson battery Isolator that allow the maximum alternator current pass through to charge your dual battery system. The factory alternator outputs 70 amps but my aftermarket Bosch alternator outputs 100 amps.
  • DC-DC chargers that do all sorts of smart stuff when charging your batteries but are limited to a fairly low charging current (eg the popular Redarc BCDC1220 only puts out 20 amps). Some even allow you to connect a solar panel to your charging system.

So ask yourself the question now. Why limit the ability of the charging system to charge your batteries? Why would I want to  charge at 20 amps and drive say 5 hours to charge my batteries when I can get the job done with an isolator and a 100 amp alternator in just one driving?

Well the reason is that about the time the Hilux Vigo/N70 came on the market back in 2005, the car industry came under pressure to reduce energy consumption to meet emissions and fuel economy targets. One trick they played was to get the ECU to reduce the alternator output voltage after a period of time from the 13.8 volts used for years down to 13.2 volts. 13.8 volts is a perfect charging voltage for lead acid batteries but 13.2 volts is not so good.

So spurred on by the example of the amazing mains powered  Ctek multi stage battery chargers and some other wannabe brands, the technology was transferred to automotive applications and the DC-DC charger was born. Back in 2008 when I set up my Hilux, these did not even exist as I am sure if they did, ARB would have done their best to upsell me from the crappy Shurepower isolator they stitched me up with.

In my view, the best system is the simplest and cheapest option and it works perfectly with my aftermarket alternator as it always seems to output 13.8 volts so an isolator works perfectly. I'm not sure if its the alternator or the auto sparky who fitted it for me that tricks the ECU into letting the alternator output 13.8 volts, but it works well .

Yeh, I know, you only have the standard Toyota Hilux alternator so it's going to reduce the voltage. Let me tell you about a really cool little trick that will let you charge your Toyota Hilux battery at 13.8 volts all day every day with a cheap as chips isolator and a cool little gadget that will only cost you $50 instead of $500 for a DC-DC charger. Just head over to ebay.com.au and search for alternator voltage booster  and choose the listing for your Hilux from a seller called hkbelect  who is a qualified auto sparky, don't grab  one of the cheap and nasty imported ones. This is a cleverly modified fuse that you pop into your fuse box on the alternator voltage sensing circuit that contains a diode. Now a diode induces a voltage drop of 0.6 volts across it so the ECU now senses a voltage of 13.2 volts when the alternator is happily pumping out 13.8 volts. This is well below the design limits of the Toyota electrics so it does no damage to your vehicle at all.

But won't my battery get overcharged?

No, not at all. A lead acid battery will only ever accept the current it need to become fully charged. You can add 47 different chargers to a battery system and the battery will just politely take what it needs and stop drinking up the current. 

But I want to use a solar panel as well

Well, that's absolutely fine. You don't need a fancy Ctek charger to do this as part of your engine battery charging  system. It is far easier and a hell of a lot cheaper to just add a dedicated MPPT solar charger and wire it in as a separate charging system. The one to get is a Tracer which you can find on eBay. There is another brand that has taken over this slot so I will update this when my electronic guru gets back from the Kimberleys in a few weeks. Lucky Sod!

But tow a caravan or camper trailer with solar panels on the roof

Even better, Just hook your auxiliary batteries into your isolator controlled dual batteries via an Anderson plug and let your caravan charging system also charge your vehicle batteries. Of course if you plug your van into mains power, an anderson plug extension lead is the perfect addition to keep your car battery  fully charged and let you park in a more convenient location. You can't do this with a DC-DC charger as the DC-DC charger prevents the charge from going back to the vehicle so the so called experts will want to sting you for a DC-DC charger in your trailer as well. 

So I had 2 Aux batteries in my Hilux and another 2 in my caravan and all of this worked perfectly driving down the road with 30 amps of solar on the van and 100 amps of alternator topping up 4 auxiliary batteries. I never needed to add the 3rd battery that there was provision for in the caravan.

But I have an absorption fridge in my van that draws 15 amps all the time

It might be unconventional but the best solution is to add a second  isolator to your auxiliary battery system and direct connect  it via a different colour anderson plug using heavy wire to your absorbtion fridge. I used a red Anderson plug for the fridge and a grey one to charge the batteries in the van. Different colour anderson plugs are not interchangeable so you can never get them mixed up. So how does this work? Well, you start your car, the cranking battery gets charged and the first isolator starts to charge you car batteries. After a while they are charged and the second isolator kicks in and starts to run your fridge. You will never have fridge problems again in you van. Well I never did anyway. The Matson isolator is ideal for this as it terminals are well protected to prevent any shorts occurring.

 conclusion

So if you follow the ideas I have outlaid in this article and correctly size the wires to your Aux batteries and camper trailer you will end up with a kick ass charging system and a few hundred dollars left in your pocket.. Hell, you might even plug a slow cooker into an inverter and cook dinner while driving down the road like one of my mates does! Believe me, this stuff works. Don't forget to buy your Hilux battery tray and Matson isolator from the VMN store.