If you regularly travel in your campervan, your engine can provide one of the most dependable ways to keep your leisure battery charged.
But on modern campervans — particularly those using lithium leisure batteries — charging from the alternator isn't always as simple as connecting the starter battery to the leisure battery.
That's where a DC–DC charger comes in.
Also known as a battery-to-battery charger or B2B charger, a DC–DC charger takes power from the vehicle's electrical system while you're driving and delivers a controlled charge to your leisure battery.
In this guide, we'll explain what a DC–DC charger does, why smart alternators matter, what size charger you might need and how options such as the Victron Orion XS fit into a campervan electrical system.
What Is a DC–DC Charger?
A DC–DC charger sits between your vehicle's starter/alternator side and your leisure battery.
Its job is to take the available input from the vehicle and convert it into a controlled charging voltage and current suitable for your leisure battery.
This is important because the voltage coming from your vehicle isn't necessarily the voltage or charging profile your leisure battery needs.
Vehicle voltage can change depending on:
- Engine operation
- Alternator behaviour
- Vehicle electrical demand
- Battery state
- ECU charging strategy
Your leisure battery, meanwhile, needs to be charged according to the requirements of its particular battery chemistry.
A suitable DC–DC charger manages this process so the leisure battery receives a controlled charge while you're driving.
How Does a DC–DC Charger Work in a Campervan?
In simple terms, the charging path looks something like this:
Vehicle Starter Battery / Alternator → DC–DC Charger → Leisure Battery
When the correct enable conditions are met, the DC–DC charger takes power from the vehicle side and uses it to charge the leisure battery.
Rather than simply allowing current to flow unrestricted between the two batteries, the charger regulates its output.
This provides two important benefits.
Firstly, the leisure battery receives a charging profile suited to its chemistry.
Secondly, the amount of charging current can be controlled rather than allowing the leisure battery to demand whatever current it can draw from the vehicle's electrical system.
The exact installation and method used to determine when the charger operates will depend on the vehicle and charger, so manufacturer instructions should always be followed.
Why Are DC–DC Chargers Important With Smart Alternators?
Modern vehicle charging systems have changed considerably.
Many newer vans are fitted with ECU-controlled or "smart" alternators.
Older alternators generally maintained a relatively predictable charging voltage while the engine was running.
Smart alternators can behave differently.
The vehicle's ECU can reduce alternator voltage when full output isn't required, helping the vehicle manage electrical load and efficiency.
That creates a problem for traditional leisure-battery charging methods.
A simple voltage-sensing relay may disconnect or fail to provide a complete charge when the vehicle voltage falls.
A compatible DC–DC charger can take the varying input from the vehicle and provide the leisure battery with the controlled charging output it requires, provided the charger remains within its designed operating conditions.
Do I Need a DC–DC Charger With a Lithium Leisure Battery?
Lithium leisure batteries are another major reason DC–DC chargers have become so common in modern campervan electrical systems.
Lithium batteries have relatively low internal resistance and can accept high charging currents.
That can be useful because it allows them to recharge quickly, but it also means the charging system needs to be properly controlled.
A DC–DC charger provides a defined current limit while delivering a charging profile suitable for the battery.
This helps ensure that the system is designed around the limits of the:
- Leisure battery
- Battery Management System (BMS)
- Alternator
- DC–DC charger
- Cabling
- Fuse protection
- Vehicle electrical system
For a lithium campervan system, controlled alternator charging is generally the appropriate approach.
Always check the requirements specified by your battery and charger manufacturers.
What Size DC–DC Charger Do I Need?
This is one of the biggest questions when choosing a battery-to-battery charger.
You'll commonly see chargers rated at figures such as:
30A, 50A and 70A
It's tempting to assume that the biggest charger is automatically the best.
It isn't.
There are three important things to consider:
1. How much energy do you need to replace?
2. How long do you normally drive?
3. How much charging current can your battery and vehicle safely support?
A campervan that drives for several hours almost every day may be perfectly comfortable with a smaller charger.
A van that spends several days parked and then only drives for a short period may benefit from faster charging — provided the rest of the system can safely support it.
How Much Power Can a DC–DC Charger Replace While Driving?
A useful early-stage calculation is:
Charging Current (A) × Driving Time (Hours) × System Voltage ≈ Energy Delivered (Wh)
For example, imagine a nominal 50A DC–DC charger operating close to full output for two hours on a 12V system.
50A × 2 hours × 12V = approximately 1,200Wh
In theory, that's around 1.2kWh of energy.
Real-world charging won't necessarily match that figure exactly.
Charging can be affected by:
- Battery state of charge
- Charge tapering
- Temperature
- Cable losses
- Charger temperature
- Available vehicle-side power
- Battery charge-current limits
However, the calculation is still useful when comparing charger sizes.
If your campervan uses around 600Wh of energy per day, for example, you can begin to understand how much driving might be required to replace that energy.
30A vs 50A vs 70A DC–DC Chargers
There's no universal charger size that works for every campervan, but these ranges can help with initial planning.
30A DC–DC Charger
A charger around the 30A mark can be suitable for:
- Smaller leisure battery banks
- Lighter daily electrical consumption
- Campervans that drive regularly
- Systems where slower charging isn't a problem
If you frequently spend several hours driving between stops, you may not need an extremely high charging current.
50A DC–DC Charger
A 50A-class charger provides faster replenishment and can work well with many medium-sized lithium systems.
It can be particularly useful if you're running equipment such as:
- Compressor fridge
- Laptop
- Lighting
- Fans
- Pumps
- Device charging
and want to put a useful amount of energy back into the leisure battery during normal journeys.
70A DC–DC Charger
A 70A charger can provide significantly faster charging, making it attractive for larger or higher-demand lithium systems.
However, 70A charging places a substantial continuous load on the system.
Before installing one, you need to make sure the:
- Alternator can support the additional demand
- Battery can accept the charging current
- BMS permits the charging current
- Cable size is suitable
- Fuse protection is correct
- Connections are appropriately rated
- Charger has adequate ventilation
A 70A charger is therefore not automatically suitable for every van.
Bigger Isn't Always Better
It's easy to look at two DC–DC chargers and assume the higher-current model is the obvious choice.
But campervan electrics need to be balanced.
If your battery can only accept 50A of charging current, there's little benefit in choosing a charger intended to provide considerably more than that.
Likewise, putting a very large continuous electrical load on a vehicle charging system that wasn't designed for it can create problems.
Cable length also matters.
Higher currents require careful consideration of cable size, voltage drop, installation method and fuse protection.
Choose the charger based on the complete system, not simply the largest number on the box.
What Is the Victron Orion XS?
The Victron Orion XS is a DC–DC battery charger designed for controlled battery charging between DC systems.
For campervan applications, the Orion XS range provides configurable charging and monitoring through the VictronConnect app.
Bluetooth connectivity means compatible settings and charger information can be accessed from a phone without needing to physically interact with the charger every time.
Another useful feature is adjustable current limiting.
Rather than assuming the charger must always operate at its maximum possible output, the charging current can be configured to suit the requirements of the installation.
This can help when matching the charger to the:
- Alternator
- Leisure battery
- BMS
- Cabling
- Overall electrical design
Compatible models with VE.Direct can also form part of a wider Victron monitoring system.
Victron Orion XS 12/12-70A
For suitable higher-output 12V systems, Nomadic Leisure stocks the Victron Orion XS 12/12-70A DC–DC battery charger.
Its higher current capability can be particularly useful in larger lithium electrical systems where faster alternator charging is required.
But it's important not to think of the 70A rating as a recommendation for every campervan.
The vehicle, alternator, leisure battery, cable route, fuse protection and installation environment all need to be assessed before deciding what charging current is appropriate.
Isolated vs Non-Isolated DC–DC Chargers
Another term you may encounter when shopping for a DC–DC charger is isolated and non-isolated.
So what's the difference?
Non-Isolated DC–DC Charger
A non-isolated charger shares a common negative path between the input and output sides.
This arrangement is common in metal-bodied vehicles where the electrical system has been designed around a shared chassis return.
Isolated DC–DC Charger
An isolated charger keeps the input and output negative sides electrically separate.
This can be appropriate for installations where a shared negative return isn't suitable.
However, you shouldn't choose isolated or non-isolated simply because one sounds better than the other.
The correct choice depends on your vehicle's earthing arrangement and the manufacturer's installation requirements.
DC–DC Charger Installation: What Matters?
The charger itself is only one part of the installation.
A powerful DC–DC charger fitted with undersized cables or inappropriate protection isn't a good charging system.
Several details need careful consideration.
Correct Fuse Protection
Appropriate fuse protection should be installed close to each relevant energy source according to the equipment manufacturer's requirements and the overall electrical design.
The fuse isn't simply there to protect the charger.
The wiring needs to be appropriately protected as well.
Correct Cable Size
Cable needs to be selected based on factors including:
- Maximum current
- Cable length
- Installation method
- Temperature
- Acceptable voltage drop
This becomes increasingly important as charging current rises.
Secure Connections
High-current DC connections need to be secure and appropriately terminated.
Poor connections can create resistance and heat.
Cables should also be routed and protected to minimise the risk of mechanical damage.
Adequate Ventilation
DC–DC chargers generate heat during operation.
The charger needs appropriate airflow and clearance according to the manufacturer's installation requirements.
Installing high-powered charging equipment in a tiny sealed cupboard isn't necessarily a good idea.
Correct Battery Settings
The charger needs to be configured for the leisure battery it's charging.
Different battery chemistries have different charging requirements.
Always use the battery manufacturer's approved charging settings rather than assuming a generic lithium or lead-acid profile is automatically suitable.
Correct Engine-Run Detection
The system also needs a reliable way of determining when charging should occur.
The exact approach varies depending on the vehicle and charger.
Follow the charger manufacturer's guidance for remote on/off, ignition detection or engine-run detection.
Will a DC–DC Charger Drain My Starter Battery?
This is a common concern.
A correctly installed and configured DC–DC charging system should operate only when its intended enable conditions are met and should be designed to protect the starter side of the system.
However, the exact method varies between vehicles and chargers.
That's why the correct engine-run or remote on/off configuration is important.
Simply assuming that a charger will automatically know when it should operate isn't a substitute for designing the installation correctly.
DC–DC Charging vs Solar
A common question is whether you need solar panels or a DC–DC charger.
For many campervans, the best answer is: both.
They solve different problems.
DC–DC Charging
DC–DC charging works best when you're driving.
The longer and more regularly you drive, the more useful alternator charging can become.
It's also far less dependent on the weather.
Solar Charging
Solar works while you're parked and doesn't require the engine to be running.
Once installed, it can quietly replenish your leisure battery whenever suitable sunlight is available.
However, solar production is highly dependent on:
- Weather
- Season
- Shading
- Panel angle
- Available roof space
This is particularly relevant for UK campervans during winter.
Mains Hook-Up Charging
A suitable mains charger gives you another way to recharge your leisure battery when you're connected to campsite or home hook-up.
For many campervans, the strongest system combines:
Solar + DC–DC Charging + Mains Charging
Each charging source does a different job.
How DC–DC Charging Fits Into a Complete Campervan Electrical System
Your DC–DC charger shouldn't really be chosen in isolation.
Imagine you install a large lithium battery bank because you want to spend several days off-grid.
That's useful — until you need to recharge it.
A well-balanced electrical system considers the relationship between:
- Daily energy consumption
- Leisure battery capacity
- Solar capacity
- DC–DC charger size
- Driving habits
- Mains charging
- Inverter demand
If you're using 800Wh every day but your available charging sources only replace 400Wh, your battery is eventually going to run down regardless of how large it is.
The goal is to create a system where you can realistically replace the energy you use.
Common DC–DC Charger Mistakes
1. Assuming the Biggest Charger Is Best
Higher charging current isn't automatically better.
Your alternator, battery, BMS, cables and electrical system all need to support it.
2. Ignoring Cable Length
Longer cable runs increase voltage drop and can affect the cable size required.
3. Forgetting About the Battery's Maximum Charge Current
Check the battery manufacturer's specifications before deciding how quickly you want to charge it.
4. Choosing a Charger Without Considering Your Driving Habits
Someone driving three hours every day has very different requirements from someone who parks for five days and then drives for 30 minutes.
5. Ignoring Ventilation
Higher-output chargers can generate significant heat and need to be installed according to the manufacturer's clearance and ventilation requirements.
6. Treating the DC–DC Charger as a Standalone Component
The charger needs to work alongside the battery, solar, inverter, wiring and vehicle charging system.
Frequently Asked Questions
Do I Need a DC–DC Charger in My Campervan?
If you want to charge your leisure battery from the vehicle while driving, a DC–DC charger is commonly used in modern campervan electrical systems, particularly where lithium batteries or smart alternators are involved.
The correct solution still depends on the specific vehicle and battery system.
Do I Need a DC–DC Charger With a Lithium Battery?
Controlled alternator charging is generally the appropriate approach for lithium campervan systems.
A suitable DC–DC charger provides a lithium-compatible charging profile and a defined current limit.
Always confirm the requirements of your particular battery.
What Size DC–DC Charger Do I Need?
Start by looking at your daily energy use, average driving time and the maximum charging current supported by your battery and vehicle.
A 30A charger may be suitable for lighter systems and longer regular drives.
A 50A-class charger can provide faster replenishment for many medium-sized lithium systems.
A 70A charger can suit higher-demand systems where the alternator, battery, BMS, cabling and installation all support the additional load.
Can I Fit a 70A DC–DC Charger to Any Van?
No.
Before fitting a high-current charger, the vehicle electrical system, alternator capacity, battery charge limit, cable route, fuse protection and thermal environment all need to be considered.
Will a DC–DC Charger Drain My Starter Battery?
A correctly designed and configured installation should charge under its intended enable conditions and protect the starter side.
The exact method depends on the vehicle and charger, so always follow the relevant manufacturer instructions.
Can I Use Solar and a DC–DC Charger Together?
Yes.
In fact, they complement each other very well.
Solar can charge the leisure battery while you're parked, while the DC–DC charger provides charging when you're driving.
Add a suitable mains charger and you have three different ways of replenishing your battery.
Choosing the Right DC–DC Charger for Your Campervan
So, what size DC–DC charger does your campervan need?
There's no single answer.
A 30A charger may be more than adequate for a lighter electrical system with regular driving.
A 50A charger can provide faster replenishment for many medium-sized lithium systems.
And a 70A charger, such as the Victron Orion XS 12/12-70A, can provide higher-output charging where the vehicle, battery and supporting electrical system have been designed for it.
The important thing is to look beyond the headline charging current.
Consider how much electricity you use, how often you drive, the size of your leisure battery and the charging limits of both your vehicle and battery system.
At Nomadic Leisure, we stock Victron DC–DC charging equipment, including the Victron Orion XS 12/12-70A, alongside batteries, solar, inverters and monitoring equipment for complete campervan electrical systems.
Not sure whether your campervan needs a 30A, 50A or 70A DC–DC charger? Speak to the Nomadic Leisure team about a complete electrical design or professional installation, and we can help match the charging system to the way you actually use your van.
