What’s a DCDC Charger, and do you need one?

There’s a lot of 4WDing and camping accessories that you can purchase which aren’t really necessary. In this post, we take a look at the DCDC charger, which has exploded in popularity.

The thing is though, do you actually need a DC to DC charger, or is it another fad that every man and his dog buys because its the new thing on the block?

I’ve long been sceptical about them, and today we cover everything you need to know about them, and leave you with the information you need to make an educated choice.

DCDC charger
Do you really need a DCDC charger?

What is a DCDC charger?

A DCDC charger takes low voltage current, and uses it to charge a secondary battery through a number of stages (bulk, absorption and then float).

In most cases, it will take 12V alternator power, and boost it to charge a battery system further away. These are different to an AC charger, which take 240V power from the wall (or a generator) and convert it to 12V for charging your batteries.

DCDC chargers are primarily used to charge a battery bank made up of one, or more batteries that are designed to be deeply discharged.

The battery banks are commonly used for running accessories like fridges, lights, water pumps, inverters and so on and so forth. They are generally hooked to the cranking battery in one way or another, and a common option is via a DCDC charger. 

In years gone by, you’d simply have the two batteries connected together using a voltage sensitive relay, which would connect the two batteries together when you were driving, and then disconnect them when you pulled up and the battery voltage dropped below 12.5 volts (or a similar voltage).

This would ensure that you could run your accessories off the ‘separate’ battery without flattening your cranking battery and not being able to start your vehicle the next day.

When you packed up and left, the alternator would charge the main battery, and then the secondary one too. 

A DCDC charger sits between your main battery and the one you want to charge, and it modifies the charge going to your secondary battery to suit it.

In most cases, it will bump the voltage up. For example, it will often take 12.8 volt power from your cranking battery/alternator, and increase it to 13.5 volts going into the batteries being charged.

There’s a number of reasons why a DCDC charger can be beneficial, which we’ll go into below.

What’s the benefit of a DCDC charger?

The 4WD marketing industry is good, but not perfect. DCDC chargers do absolutely have a number of benefits, and if they didn’t, they probably wouldn’t sell like hotcakes.

They are however, not an absolute must (despite what some people will tell you), and we go into this further down.

It accommodates voltage drop

When you run an electrical cable, you’ll experience some form of voltage drop. This is amplified when you have a long cable run, or one that has been sized slightly undersize. For example, on my folks Pajero, we get 14.3 volts at the cranking battery when the vehicle is running.

If you measure it at the rear Anderson plug (at the back of the vehicle) its dropped down a little, and by the time you get to the caravan battery setup, its dropped even further. 

DCDC battery chargers should be installed as close to the battery (or batteries) that are being charged, so there is no voltage drop for the charging phase. Voltage drop can hugely affect your batteries ability to be charged, as by the time the power gets to the battery it has often lost a chunk of its ‘strength’.

Dmax canopy electrical work
Voltage drop is a common reason for installing a DCDC charger

It will charge a secondary battery system even with a smart alternator

Vehicle technology keeps on advancing, and there are often times when it has some unfavourable outcomes for different types of owners.

One of the ways that manufacturers have tried to save fuel is to install smart alternators, which essentially reduce the amount of charge your cranking battery gets, so the alternator is running less, and using less fuel.

This is good in terms of fuel, but it can hugely reduce your battery life and it makes it almost impossible to charge a secondary battery setup without a DCDC charger.

The reason is simple; by the time the power gets to your secondary battery its not high enough to actually charge your deep cycle battery as the volts aren’t high enough.

Some smart alternators can be turned off, or you can install diodes to bump the voltage up, but the most common path around it is to fit a DCDC charger, which takes the low voltage power and bumps it up to a suitable level.

They automatically isolate

You need to be able to isolate your cranking battery from your auxiliary battery setup. If you can’t, or don’t, there’s a chance you’ll wake up to a flat cranking battery.

Beyond this, your cranking battery isn’t usually designed for slow, small power draw and when all batteries are hooked up together it will deplete at the same rate as your auxiliary batteries that are designed to run appliances for long periods.

Redarc VSR
If you have a DCDC, you don’t need a VSR like this Redarc SBI12

They accommodate battery chemistry differences

One of the more important things about a DC to DC charger is that they can charge different types of batteries.

Different batteries require different charging profiles, and most DCDC chargers can be adjusted to suit the type of battery that you are running.

This is particularly the case if you are running a 12V lithium battery, but even if you are running an AGM, Gel, Wet or Calcium its important to have the right charger for the job.

Blue Nova Lithium
If you have lithium batteries, you should be using a lithium specific charger

They use the best charging profile for your batteries

Going on from the above, not only does a DCDC use the correct charging profile for your battery type, but it also adjusts the charge based on what the battery is doing.

They are not a trickle charger, or a dumb charger that just pumps the same current into your batteries all day.

They monitor your batteries voltage, and even sometimes temperature and adjust the charge to bring them to full in a way that is efficient, safe and isn’t going to make your battery explode!

Who sells DCDC chargers?

There are lots of DC to DC charger manufacturers out there.

The most common units are Redarc and Enerdrive. However, you can get them from Renogy, Projecta, Intervolt, CTEK, Australian Direct Thunder, Ridge Rider, Adventure Kings, iTech and the list goes on and on.

They are not all the same, and in many cases vastly different in quality, and what they can do (and even what you can do with them!).

The best DCDC charger is the one that fits your budget, and does what you need it to reliably. There are certainly some better brands than others, so do your research before laying any money down.

What to look for in a DCDC charger?

I mentioned above that DCDC chargers are not all the same. There’s a few things that you should consider before laying your hard earned coin out:

Is it a good quality unit?

Like anything in life, you can buy the cheapest DC to DC charger and hope for the best, or you can buy the most expensive one out there and expect it will last a long time.

We generally fall in the middle, but always look for reviews from real life owners to see what they think of it. 

Some have fantastic reputations and are highly recommended, and others are 50/50 as to whether you’ll have issues in the first few years!

What battery types will it work for?

When we purchased our Projecta DCDC, I never thought about the possibility of fitting lithium in the future.

It’s not a lithium compatible DCDC (they do sell them now though), which means when our AGM finally dies and we go to lithium (which we’ve now purchased but not installed) I’ll not only have to change the battery, but I’ll need a new DCDC too.

Have a think about how long you plan on using the charger for, and whether it does the different chemistries that you are likely to run.

Itech Lithium Battery
If you plan on going to a lithium battery, your needs change in terms of a DCDC

What’s its maximum charge rate?

One of the most important things to think about is the maximum charge that the DCDC can do. Some are capped at 15 amps, whilst others are capped at 25, 30, 40 and even 50 amp. 

If you get an undersized DCDC, you’ll have to drive for hours every day to charge your batteries up, as they are literally capped at the maximum charge rate. On the other side of the coin, don’t get one that will damage your batteries because its too big for your setup.

Can you adjust any settings?

Going on from the above point, being able to adjust the settings is magic, and some DCDC chargers do this very, very well. Our Enerdrive DC2DC for example, is as customisable as it gets, and is one of the reasons I seriously rate it.

Not only will it do any battery type (including lithium), but you can adjust the maximum charge rate and a whole heap of other settings based on your requirements. 

I’ve bumped the charge rate up a little for our two AGM batteries when we were struggling to keep up a while back, and when we move to lithium I’ll change it to the lithium profile and bump it to maximum charge (if the cables are rated for it!).

A DCDC that you cannot adjust any settings on can be extremely frustrating, and in many ways restrictive, and even sometimes plain useless.

Projecta DCDC
Many DCDC Chargers have virtually no adjustment ability

What else does it come with?

Today, you’ll find DCDC battery chargers often come with other items. The Redarc Manager 30 is a good example of this, as its an all in one charger, and management system.

They have an ACDC charger, DCDC charger, MPPT regulator, battery monitor, isolation system and so on and so forth. They are also significantly more expensive, and yet are one of the most common items used in higher level fit outs.

Some require you to have additional solar relays, and other equipment in order to install the DCDC and make them work, so ask a few questions before you buy.

Is it waterproof?

Some DCDC chargers are waterproof, and dust proof. Others are not in any way, shape or form, and this is an important consideration. It’s not uncommon to see DCDC chargers mounted near the radiator at the front of a 4WD, where they get good air flow but are subject to a heap of dust, mud, and water.

On the flip side, a lot of people mount them in nice electrical boxes that are dust and waterproof themselves (or mounted inside a vehicle). Don’t make the mistake of getting a charger that isn’t waterproof with the idea of mounting it outdoors!

DCDC waterproof
If it can get wet, you need to ensure its waterproof, or mounted somewhere suitable

How does it cool?

DCDC chargers work pretty hard. When our Enerdrive unit is really working, you’ll hear the fan come on and roar from a distance.

Heat is one way to destroy anything, and a good cooling system will make a huge difference to the lifespan of your DCDC. Some do not have any fans at all, and just rely on heat dissipation through the fins.

What’s the warranty and after sales support like?

Again, brands can be worlds apart here. Redarc has some of the best warranty and after sales support for any 4WD or camping product period. Other, cheaper brands require you to fight a lot harder to make any progress.

Do not underestimate the importance of technical support either. These units can be frustrating to make work, and require some assistance from the OEM.

You can ring the Redarc technical line and have support within minutes during business hours. Good luck doing that with many of the cheaper end products!

Does it have solar input?

In years gone by solar charging was done by a separate unit. Today though, many good quality DCDC chargers will come with a solar input (although you can get them without it, so watch out), and you simply feed your alternator power in on one side, and other solar power in on the other.

If it does have solar input, make sure that it matches the panel that you want to run. Some will not take more than 23V, which rules out running old house panels, or even higher voltage panels (like the Enerdrive options).

The Enerdrive DCDC will do up to 43V, which means you are able to run a much greater range of solar panels.

Check out how good the solar input is too, and when it comes on (as in choosing between the alternator and solar).

Some don’t do a good job with solar and you are better off with a quality MPPT regulator on its own.

Solar input into a DCDC
Does the DCDC have solar input?

DCDC charger price

DCDC chargers start off at about $160, and work their way up to around $800. That’s a massive variance in price, and somewhere along the line you have to decide if the extra price is reflected in quality. 

What cable size will you need, and where are you going to mount it?

Don’t buy a DCDC without being sure of where you are going to put it, and what cable size is needed.

If you are getting an auto electrician to install it then the cable size will be sorted out by them, but its important to fit the right size cables to ensure you don’t make the DCDC work harder than it needs to, create additional heat and even potentially cause a fire.

If you are putting 50 amps of charge into a lithium battery from a DCDC its going to be taking a huge chunk of power from your alternator, which could be 6 + metres away and that means a significant cable size is needed.

Cable sizing for a DCDC
Make sure you use the correct size cabling for the job

Alternatives to a DCDC charger

DCDC chargers are relatively new, and people did not use them many years ago. You can get away with a simple manual isolator, Anderson plugs that you remove each time you pull up, or a voltage sensitive relay that disconnects the batteries from each other.

None of these allow you to run different chemistry batteries together though, and you will get voltage drop over a long run.

Some people just rely on solar with a decent MPPT or PWM regulator to keep their batteries topped up, and there’s nothing wrong with that either.

A lot of caravans will have an Anderson plug that goes to the van batteries to charge it while you drive, and then a solar input.

The vehicle can do some charging while you drive (but it struggles to do the higher voltages as it has dropped so much by the time it gets to the van batteries) and the solar finishes it off.

Itechworld regulator
A lot of people just use the alternator and a solar regulator

On our old camper trailer, we had so much solar that I probably only plugged the DCDC in a handful of times in the several years that we owned it, as the solar kept the batteries healthy enough on their own.

Can a DCDC slow your battery charging down?

Yes, it absolutely can slow your battery charging down, particularly if you have a large battery bank that will accept a lot of charge.

DCDC chargers are getting larger and larger in capacity today so the problem is being reduced, but if you have 120+ usable amp hours (240ah of AGM or 110ah of lithium) there’s a good chance that a smaller DCDC will slow your battery charging down.

This is mainly in the bulk stage, where the battery bank would be able to accept more charge than the DCDC can output. For example, if you had a big battery bank hooked up to a 25 amp DCDC, it would charge much faster connected directly to your alternator (which is usually rated between 80 – 140 amp).

Our old camper trailer had a 15 amp DCDC (one of the original Projecta units), which meant to charge the 50 – 80 amp hours we’d use in a day, we would have to drive for 3 – 5.5 hours a day, which is impractical.

The flip side is that once your batteries are done with the bulk charging stage, it can take much longer to charge them without a DCDC, so there is some balance.

Battery voltage
A small DCDC can certainly slow your charging down compared to the alternator only

Installing a DC to DC charger

The installation of a DCDC charger is usually fairly simple, but it needs to be done well, legitimately and safely with the correct fuses in place.

These move a fair chunk of current, and will comfortably cause your vehicle (or trailer) to go up in flames if its not done correctly.

We’d always advise you consult or use an auto electrician, but many people do DIY.

Do you actually need a DCDC charger?

For many applications, you don’t need a DCDC charger, and you would get away with a VSR, or a good solar setup.

However, if you are running different chemistry batteries, or your batteries are expensive, or you just want a simple setup that always works as best as possible for your batteries, they are a good idea.

In the scheme of many 12V electrical setups today they are quite cheap, and easily justifiable. However, if you have a cheaper, or more simple setup and you are still able to sufficiently charge your batteries from solar or the alternator you do not need a DCDC. It might improve things, but its not a must.

I get frustrated when I see things marketed as a must have when they really aren’t, and for many people you can still comfortably get away without one.

It might not be the best for your battery system, and for many scenarios they are well and truly justifiable, so think about your own setup, and get one if you feel its needed.

If you don’t feel its needed, then by all means don’t bother with the marketing hype!

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  1. Hey Brian,

    My understanding is that if it has an equalisation stage, its not really a lithium profile. Can you adjust the time that its on for, down to zero minutes?

    Given the expense of lithium batteries, I would be getting a charger that you are confident in, or going back to Sunyee, and asking them for further information.

    Alternatively you could ask Fusion for their advice, or speak to a dedicated auto sparky.

    All the best mate

  2. Brian Cameron says:

    Hi Aron.Ive been running 2x100ah agm batteries and I have an Atem Power 40amp dc to dc charger that can be changed to lithium but has automatic equalisation that can’t be turned off. I’ve just bought 2x100amh fusion lithium batteries and don’t know if I can still use it or do l need to get a dedicated lithium dc to dc charger. I’m running a 170w solar panel on the van and use my portable 120w panel when stopped and just connect straight to lithiums it has a regulator still attached. If l do away with the dcdc then l have nothing to isolate my cranking battery. I don’t know what to do can you help me please mate regards Brian

  3. Hi Mark,

    The DCDC’s do the charging, but won’t provide a display. You can use a basic volt meter if its an AGM, or install a shunt, or go for a management system. There’s lots of options out there.

    We’ve just installed a Renogy shunt and display, which has been hugely helpful to see what the battery is doing


  4. mark grooby says:

    Hi, if I have a DCBC Redarc (Battery Controller) set up in my hybrid (say older 2015-16 model) is there a way to see my battery capacity. I think a lot of systems do not have a display like say the BMS 30 gives you.

  5. Hi Helen,

    A Redarc 1220 is a DCDC charger, and has nothing to do with the electric brakes. The electric brakes should be a little knob on your dash that is blue when you are driving, and pink/red when you brake. If you don’t have this, you need to get one fitted.

    When you say car batteries, are you referring to the main starter battery under the bonnet, or a secondary one somewhere else? What batteries are you buying?

    The Redarc 1220 shouldn’t be doing anything if you aren’t towing, and its set up to only feed the caravan batteries.

    I suspect you may have a fault that is causing an issue. A good auto electrician is the place to start, or you can call Redarc; they have exceptional customer service and would be more than happy to help you out.

    It’s very hard to help without further information

    All the best

  6. We bought a small caravan about 5 years ago and it required us to have an electronic brake controller installed in our Captiva. The auto electrician installed a redarc 1220 and an Anderson plug. I have no idea if this was what is required to operate electric brakes, but what I do know is that we have gone through 3 car batteries since we’ve had this thing. I really need some impartial advice because no one seems to be able to tell me much. Can I have a switch installed that can turn off the redarc when we don’t need it? We only use the van 2 or 3 times a year for short trips, but it’s costing us a fortune in batteries, not to mention the inconvenience of not knowing if the car is going to start on any given day.
    Help please.
    Thank you in advance.

  7. Hi Liam,

    I would measure the voltage at the rear Anderson of your vehicle with the car idling, and revving a little and see how high it is. If it doesn’t have a smart alternator it should still charge the battery while you drive, and potentially even at a similar rate to a DCDC. If its low, it wont charge much and you are better off with a DCDC.

    If your 200W solar panel keeps up with demand, you might not even need any charge from driving around. You can get DCDC chargers that put more than 30 amps in, but again, it all comes down to your use, and a 140aH battery probably wouldn’t like taking that much charge anyway.

    I’d give it a whirl, and monitor the voltages of the battery and see how it goes.

    All the best

  8. Very informative. I have just installed a 140ah AGM in my camper trailer and DCDC was the next consideration. However, the trailer is only getting occasional use, and even then we’d only be going no more than 3-4 hours from home. I have a 200W solar panel for when stationary.

    My question is, are the DCDC really only useful if you are driving round all day or going on long trips? From what I can find online, regardless of amps the DCDC puts out you are looking at 5-7 hours for it to fully recharge the battery (which has a 30A charge limit anyway) so in my situation would I really need it? I was thinking I could get away with just putting it on a smart 240V charger when I get home. I could also leave it on trickle solar at home but I’ve heard this isn’t necessary for AGMS.

  9. Hey Chris,

    I hate to give advice without being able to see it; if I misunderstand what you are saying then it won’t be good for either of us.

    If you aren’t moving, and you plug a regulated panel onto your rear battery, it will top that battery up only, as the VSR should stop any charge going elsewhere (unless its still open).

    However, you can also plug it into the front battery, and that will top this up your main battery until your VSR opens, and then it will charge both batteries together, until they reach full. That’s what I used to do with our 80 series Land Cruiser setup, with alligator clips on the main cranking battery terminals.

    All the best

  10. Thanks very much for this article. Very interesting.
    Similar situation to James here, but if i bring power into my canopy from alternator via anderson with VSR (i dont have a smart alternator), can I plug my MPPT solar regulator into my Control Box/Power Box input and still charge the battery when the vehicle isn’t moving via solar blanket? Thank you

  11. Thanks Aaron, good to know. I’m thinking along same lines as you DCDC ain’t always necessary, so might try a simple MPPT in my canopy only and see how we go!

  12. Hey James,

    You can run your solar without a DCDC, as long as you have a decent regulator (MPPT or PWM). It will not over charge; the solar regulator will work in conjunction with the alternator to charge your rear batteries.

    As per the article, a DCDC is only really needed to boost the voltage, which if you have solar, isn’t actually needed either, to do the top end of the charge

    All the best

  13. I guess the main reason to use a DCDC charger is to have both alternator and solar input connected at the same time and the DCDC charger to figure it out.
    I’ve got an Anderson connection from my alternator to canopy on a VSR, to charge an aux battery. Also looking to add solar now, not sure if I can add only an MPPT controller (or need a DCDC), as having the 2 charging sources potentially running together could lead to overcharging?

  14. Hey Matt,

    I’m glad you found it useful. No need to get something if you don’t need it!

    All the best

  15. This was the most useful article to clarify up the issue. My system is very very simple in a motocross van and the cost of a DCDC charger alone would of come close to pretty much the entirety electrical set up minus batteries. Thank you!