What is a DC-DC Battery Charger: All You Need to Know

By: Scott Adamson
/ July 14, 2022
Are you curious about a DC-DC battery charger and how it can benefit your campervan? Let’s find out.

A stable supply of electricity in your van is vital, especially for long trips. It lights your van, powers up your switchboards and sockets, and activates your fridge, heating system, and water pumps.

There are several ways to charge your campervan batteries. The main ways to do that are:

  • Alternator (DC-DC)
  • Solar, and
  • Shore Power (Plugging it in); this requires you have an inverter/charger.

One component that raises a lot of questions is the DC-DC battery charger. What is a DC-DC battery charger and why do you need it?

In this article, I’ll cover the following topics: 

  • What a DC-DC battery charger is, its function, and its importance.
  • A quick comparison between the DC-DC battery charger and other alternatives.
  • Several popular brand choices for DC-DC battery chargers.

So, without further ado, let’s get right into it!

What is a DC-DC Battery Charger?

In layman’s terms

Your vehicle’s alternator is what creates the electricity and charges the vehicle battery while you’re driving. 

When you have a campervan, you use that same alternator to charge your house batteries. These are the batteries that are used to power the components inside your campervan (lights, etc) and generally, these will be Lithium or AGM batteries

By default from the factory, your alternator is set up to know when your vehicle battery is charged and how much power the alternator needs to put out. It’s not designed to know about the campervan conversion you have going on in the back.

That’s where the DC-DC Battery Charger comes in. 

Why do You Need a DC-DC Charger? 

The reason you need a DC to DC charger is that most of the time your vehicle battery is a lead acid battery, so your alternator is designed to charge a lead acid battery. The charging profile to charge your house battery is different. So the DC to DC charger tells your alternator:

  • What type of house battery do you have, and
  • What are the charging requirements

In short, the DC-DC Battery Charger is the brain that tells your alternator how to properly charge your house batteries. 

Alternator -> DC-DC Battery Charger -> House Battery

Direct Current (DC) Explained:

Let’s also talk about DC (direct current) in more detail. Direct current, more commonly known as DC, is known for its constant voltage flow. In contrast, AC (alternating current) has a changing flow of voltage.

While most of our home appliances still work on AC, DC is more efficient and popular in small cars, boats, and vans. With the soaring popularity of solar power in vans, DC and DC-DC battery chargers have emerged as important players.

Here’s how it compares.

  • A DC-DC charger (also known as a battery to battery charger) converts the output from your primary battery and charges your secondary battery using optimal charging.
  • Most typically, a single battery or a system of batteries is used to store the converted power.
  • You can use the secondary batteries powered by a DC-DC charger for minor purposes (charging cellphones) and running major appliances such as your fridge.

Pro-tip: If you are an on-the-go van lifer travelling miles on the road, you can charge your secondary battery via the DC-DC converter quite efficiently.  

How Does a DC-DC Battery Charger Work?

The DC-DC battery charger uses your van’s alternator (an electrical generator) to convert the available power. It then converts that power to a higher voltage (Ah) for your secondary battery (i.e. your house battery). 

Here’s how the DC-DC charger uses a 3-step process to charge your battery optimally.

  1. Bulk: In this step, the DC-DC battery charger converts the current from the alternator and fills in the secondary battery almost to the maximum. 
  2. Absorption: Here, the power levels off and stabilizes so the battery doesn’t ‘overcharge’. 
  3. Float: This occurs when the battery is fully charged with its optimal capacity reached. 

What are the Benefits of Using a DC-DC Charger?

Now that you have a good idea about DC-DC chargers, let’s look at a few benefits of installing one of these.

1. Overcome Issues With Smart Alternators

Most vans now come with smart alternators designed to minimize power output. This means they cannot charge a secondary battery with their load restriction. A DC-DC converter takes care of this problem by isolating the main battery from the alternator. 

2. Maximizes Main Battery Charge

Another benefit of installing a DC-DC battery charger is its ability to maximize the charge of the main battery. The charger can convert an amperage of as low as 9 volts up to 13.5 volts to charge the main battery quickly and efficiently. You can get close to 100% charge on your main battery with a good day of driving.

3. Works Without Solar Power

DC-DC chargers are also a blessing in disguise if you mainly travel in areas without a lot of sunlight. DC-DC chargers can help charge the auxiliary battery to power your gadgets without worrying about solar power or other energy backup options.

4. Adapts to Different Batteries

One of the most important benefits of a DC-DC battery charger is that it adjusts for different battery types. This is useful as it can save you the time and cost of buying a different charger every time you replace your battery.

A DC-DC charger also adjusts the power based on what the battery is used for, minimizing damage to the battery through overcharging.  

Can I Use a DC-DC Charger with Lithium Batteries?

Yes, you can definitely use a DC-DC charger with lithium batteries as it can optimize your battery life. A DC-DC charger can also extend your lithium battery life. 

Here’s how it compares.

  • Lithium batteries absorb the maximum amount of power available which can quickly become an issue if you are charging directly from an alternator. This is because if the alternator already has a significant load, the lithium battery will add to this load, causing the alternator to burn out.
  • A DC-DC charger effectively manages the power input in a lithium battery, making sure it doesn’t heat up when overcharged.
  • These batteries also have a different restart process and specific battery chemistry, making it difficult to charge them through alternative means such as an alternator.  

If you are still deciding between AGM v Lithium batteries, this informative article can help you make the right decision: AGM vs Lithium, Which Battery is best for Van Life?

What Size DC-DC Charger Should You Get  

Most commonly, batteries up to 200Ah require a DC-DC battery charger of around 25Ah. For ampere-hours exceeding 200, a 40-ampere DC-DC battery charger will work better. 

If your alternator has a 200 amp rating, you’d want to take that number, and cut it in half and that would be the charged power. The reason it’s recommended to run it at 50% is that you never want your alternator to be running at its maximum output load because it’s really hard on the alternator and it wears them out.

To select the best size for your DC-DC charger, you should consider the following: 

  • Alternator Size: Typically, alternators range between 60 to 150Ah while DC-DC chargers vary between 6 to 40Ah. You need to get a larger charger for optimal usage if you have a high-powered alternator with more capacity. 
  • Battery Type: A DC-DC charger rated 20% of your battery’s amperage would work fine for conventional batteries such as AGM and lead-acid batteries. With a lithium battery, you can go higher, to almost 30% of your battery’s rated amperage. 
  • Voltage: It is recommended to match your charger with your van’s electrical system. For example, if you have a 12-volt system (which is most common), you should go for a 12-volt DC-DC charger. 
  • Usage: Your energy usage also plays a part in determining your DC-DC charger size. If you use several appliances with your auxiliary battery, you will need a DC-DC charger. 

Popular DC-DC Charger Brands and their Cost 

Now that you have an idea of how DC-DC battery chargers work, you may wonder which is the best brand to buy. To give you a heads up, several good brands are out there catering to different customer needs. 

Here’s how they measure against each other. 

Red Arc (Our Recommendation)

In my opinion, Red Arc is the brand that you should go for. There are a few key features that set this brand apart.

  • It works smoothly with several battery types, including GEL, AGM, and lithium. 
  • Includes additional features such as solar regulation, allowing users to prioritize charging options from different power supplies (solar vs. battery).
  • It has a reliable built and can stand up to extreme temperatures and climate. 
  • Works with both 12 volts and 24-volt system

Price: The REDARC Electronics Dual Input 25A in-Vehicle DC Battery Charger costs around $410.

Victron

Victron DC-DC chargers such as the Orion-Tr Smart isolated/non-isolated are one of the most popular brands in the market right now with the following features:

  • Works well with both 12-volt and 24-Volt systems and lithium and lead-acid batteries.
  • Includes Bluetooth so you can control the power settings from the comfort of your cellphone via an application. 
  • It is durable and can adapt to high temperatures. 

Price: The Victron Orion-Tr Smart 12 V 30 Amp Non Isolated costs around $230.

Sterling

Sterling is another popular name that many van enthusiasts choose when it comes to DC-DC battery chargers. Here are its key features:

  • It comes in three variations: 40 A, 70 A, and 120 A with a 12 Volt option, hence catering to a large variety of customers
  • Works well with smart alternators with an in-built vibration sense mode. 
  • It is Lithium compatible and includes a low-temperature trip for lithium-ion batteries. 

Price: The Sterling Power Pro Ultra Charge costs $350 with a 5-year warranty. 

Renogy

Renogy is known for its cheap yet decent quality in the market. Here are some of its best features: 

  • Its flexible design ensures the safety and improves usability in different conditions. 
  • Renogy offers several layers of safety, including over-voltage and reverses polarity protection, safeguarding the batteries from overcharge. 
  • It is compatible with lithium, lead-acid, and AGM batteries. 

Price: The Renogy 12V 40A DC to DC costs around $160, while the Renogy 12V 60A Dc to Dc costs approximately $200. 

Key Takeaways

Here’s a brief overview of what this article discussed:

  • The DC-DC Battery Charger is the brain that tells your alternator how to properly charge your house batteries. 
  • A DC-DC charger can maximize charging to 100% and optimize your auxiliary battery’s life.
  • Lithium batteries work well with DC-DC chargers as it efficiently manages the power input. 
  • A DC-DC charger size depends on your usage, voltage, and battery life. As a general rule of thumb, a 200 Ah battery requires a 25 A DC-DC charger, while bigger batteries require a 40 A charger.
  • Recommendation: You should choose RedArc to buy the best DC-DC charger suited for your needs. 

Now that you have sufficient knowledge on this subject, you can confidently choose the best DC-DC charger that suits all your needs!

Scott Adamson
Wanderful Idea Guy
Coffee drinker, adventure seeker, below average photographer.
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