DC to DC Charger Buying Guide (Updated for 2025)
- Chris Wallace-Tarry
- 3 days ago
- 12 min read
The days when a simple voltage‑sensing relay (VSR) could keep a campervan’s leisure batteries happy are over. Modern lithium packs demand tighter charge profiles, alternators are smarter, and 24V systems are creeping into the van‑life scene. Enter the DC to DC charger, also called a battery‑to‑battery (B2B) charger or smart charger. By intelligently negotiating between engine and battery, a quality B2B charger tops up your batteries more quickly, more safely, and more efficiently than any traditional campervan split charger.
This guide breaks the buying decision into plain‑English steps. First, we’ll calculate the right charger size by balancing alternator output and leisure battery specs. We'll go into headline specs like peak efficiency, built‑in Bluetooth, cooling, and whether a DC‑DC charger with solar input is worth the extra spend. To finish, we’ll shortlist the devices that actually deliver, including our recommended VSR for legacy setups, the best overall DC‑DC charger, the sweetest budget pick, and a ready‑to‑install DC‑DC charger kit that makes wiring almost fun.
If you're just getting started, make sure you read our full guide on split charging systems. In that article, we go in-depth into how they work, electrical regulations, and how to wire them up.
Index
Shane, the founder of The Van Conversion, is a campervan professional dedicated to helping people transform ordinary vans into homes on wheels. He has authored Roaming Home, and teaches The Van Conversion Course, guiding many people through their van builds. Shane also writes The Van Conversion Newsletter, where he shares practical tips and insights. After completing two van builds and living on the road full-time since 2020, he is passionate about sharing his expertise with others.
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Our Top Picks
If you're anxious to get your DC to DC charger ordered, these are our top picks. They're all high-quality devices from reputable manufacturers with comprehensive safety features, high efficiency ratings, and Bluetooth connectivity.
Best Budget Setup | Best Budget DC-DC Charger | Best Overall DC-DC Charger | Best DC to DC Charger with Solar Input | Best DC to DC Charger Kit |
Sunstore Smart VSR Kit | Renogy 12V DC to DC Charger | Victron Orion XS Smart DC-DC Charger | Renogy DC-DC Charger with MPPT | Victron Orion XS Kit |
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Our favourite DC to DC charger is Victron's 50A Orion XS. It offers the highest efficiency rating we've seen at 98%, as well as built-in Bluetooth and seamless integration with Victron's GX monitoring ecosystem. A sterling reputation backed up by a 5-year warranty seals the deal.
Choosing Your Split‑Charging System: VSR vs. DC‑DC Chargers
As we explain in our full article on split charging systems, a split‑charge link lets your engine's alternator charge your leisure batteries while you drive. Along with solar power, it's an essential part of any off-grid electrical system. Until recently, that role was filled almost exclusively by the voltage‑sensing relay (VSR): a simple switch that closes when the starter battery is fully charged, diverting engine power to your leisure batteries. For classic alternators and flooded or AGM leisure batteries, a VSR is cheap, silent, and gives negligible voltage drop, perfect for the “couple of lights and a coolbox” weekend van.
The catch is that a VSR cannot regulate current or voltage. Whatever the alternator produces flows straight into the leisure battery. That brute‑force approach is harsh on lithium battery chemistry and overloads modern smart alternators that deliberately lower their output to cut emissions. Our friends at Vunked put together a simple guide to checking your van for a smart alternator:
Enter the DC to DC charger, also called a battery-to-battery, B2B, or smart charger. Instead of simply connecting the two batteries, a DC to DC charger takes the alternator feed and converts it into an optimised charging curve tailored to your leisure battery type. The unit limits current to a value you set based on your alternator output, saving your alternator from overheating, and boosts low‑voltage smart alternator output up to your battery's correct absorption voltage. A modern battery to battery charger might have built-in Bluetooth monitoring, and high-quality ones exceed 95% peak efficiency. In short, they provide faster charging whilst protecting your smart alternator and lithium leisure batteries.
Is a DC to DC Charger Always Better?
For any van with a smart alternator, any system running lithium, and anyone who wants remote monitoring, the answer is a clear yes. Prices have fallen far enough that a 30A DC to DC charger now costs little more than a branded high‑current VSR and fuse kit.
Still, there are scenarios where the humble VSR makes sense:
a pre‑smart‑alternator van, and
a small, 70–100Ah AGM leisure battery, and
a charging routine limited to short, infrequent top‑ups
In that niche, the simplicity and near‑zero standby draw of a VSR can justify sticking with the old school. If your installation fits that description, we recommend Sunstore's Smart VSR kit. The kit comes with the VSR itself, plus all the wiring, fuses, and cable lugs you'll need, all sized just right.
For almost every other modern campervan build, a DC-DC/battery to battery charger is the smarter, safer, and most efficient way to keep the lights on and the lithium happy.
Sizing Your Battery to Battery Charger
Pick a unit that’s too small and you’ll limp‑charge for hours; go too big and you’ll cook the alternator or waste money on amps you can’t use. As we explain in our split charging guide, the sweet spot lies where alternator headroom, battery chemistry, and bank capacity overlap. For a quick answer, punch your numbers into our DC to DC charger size calculator. For the theory, keep these guidelines in mind:
Alternator Current Output Current
Use the continuous rating marked on your smart alternator, or find it by searching for your vehicle on a site like Euro Car Parts. Subtract 25% from that number, as we want to dedicate some power for vehicle electrics and battery recovery. The remaining 75% is your safe ceiling.
Leisure Battery Maximum Charge Current
This is based on your battery bank size:
AGM and gel: maximum charge current = 20% of capacity in Ah
Lithium: maximum charge current = 65% of capacity in Ah
Check your battery's spec sheet to confirm these numbers. Your DC to DC charger's amp rating should never be bigger than this figure.
Assuming we have a 150A smart alternator (common for panel vans), our limiting factor is going to be our battery bank size. If we have a 200Ah AGM battery bank, our maximum charge current will be around 20% of 200, or 40A. In this case, we'd recommend Victron's 30A Orion DC-DC charger for its built-in Bluetooth and exceptional efficiency rating.
If we instead have a 200Ah lithium battery bank, our maximum charge current is 65% of 200 or 130Ah. This gives us plenty of headroom to install Victron's 50A Orion XS DC to DC charger, which gives us Victron's highest-ever efficiency ratings at 98% and GX monitoring ecosystem compatibility.
Run our calculator, confirm the result against these checkpoints, and you’ll land on a DC‑DC charger that charges fast, protects your alternator, and grows with your system.
Key Features of DC to DC Chargers
Not all DC to DC chargers are created equal. The best units pack in hardware and firmware that boost charging speed, extend battery life, and keep your van’s electrics safe. Prioritise these features when you shop:
High efficiency ratings
Multi-stage, battery chemistry-specific charging profiles
Safety features
Quiet cooling
Bluetooth and CAN-bus connectivity
Possibly, variants that incorporate MPPT solar charge controllers
Efficiency and Charging Profiles
Efficiency matters because every percentage point below 100% turns into heat instead of amp‑hours. A 90% efficient battery to battery charger delivers 90A to the battery for every 100A it draws from the alternator; the other 10A vanish as heat that stresses electronics and wastes fuel. The best DC to DC chargers have efficiency ratings in excess of 95%, like Victron's Orion XS range. They achieve those numbers with multi‑stage, chemistry‑specific charging algorithms, which charge your battery in different stages depending on its chemistry and state of charge. These smart profiles cut run‑time and heat, boosting efficiency and the lifespan of your leisure batteries.
Safety Protections
A good DC to DC charger incorporates safety features to prevent dangerous malfunctions. My van's electrics are installed under my bed; I'd never be able to sleep at night had I installed components that didn't have the following protections:
High temperature: prevents my batteries from charging or discharging beyond a safe temperature range
Over- and under-voltage: protects my batteries from over- or under-charging
Short circuit and over-current: protects my system in the event of a short circuit, acting as a redundant safety measure in addition to my fuses
Reverse-polarity: saves the device if leads are attached backwards
Quiet Cooling
It may not seem like much, but it's worth paying attention to. I've lived in a van with a shoddy DC-DC charger whose fan ran loudly long after I'd turned off the engine. Both Victron and Renogy offer DC to DC chargers with efficient, fan-less cooling which operate silently.
Bluetooth Connectivity
It's useful to be able to monitor your DC to DC charger's function as it runs to see how quickly it's charging your batteries. Additionally, advanced features like custom charging profiles are best fine-tuned from your phone or computer. This is where DC-DC charger connectivity comes in. Bluetooth-enabled models allow you to connect to your charger with your phone, monitoring and controlling it in real time.
In addition to Bluetooth monitoring, Victron take things a step further with their 'interconnected ecosystem'. The chargers in their smarter Orion XS range share VE.CAN or VE.Direct common communications outputs with other Victron devices. Connecting your DC to DC charger to your battery monitor system in this way allows it to see your battery's state of charge and tailor its power draw accordingly.
You can also connect all of your Victron devices to a GX device like the Cerbo. The Cerbo collects information on all of your electrical components and displays it as an integrated dashboard on-screen or in the remotely-accessible VRM. This way, you can monitor your whole system's status and performance in real-time, seeing how all of your components interact. You can also see historical data like power usage over time and solar production visualised as graphs, and set up rules and settings for your entire integrated system.
Combined DC-DC Chargers and MPPT Solar Charge Controllers
DC‑DC chargers with a built‑in MPPT promise one box, one fuse set, and less wiring, saving you money and simplifying your installation. They essentially share their current rating between input from your alternator and from your solar panels. In practice, this usually works by automatically shutting off solar generation when your engine's running.
This current sharing is the catch with these combined units. A 50A combined charger-MPPT caps alternator and solar input at 25A each, or 50A from one and nothing from the other. This means that if you've got a normal-sized van with a 150A alternator and more than 250W of solar, you won't be using their full potential when the engine's running.
For small vans, however, a DC to DC charger with solar input is perfect. Small, 90-120A alternators can't spare the full 50A to run a standalone DC-DC charger of this size. A small-roof solar array of 200-300W produces about 16-22A of power. Therefore, a 50A DC to DC charger with solar input like Renogy's can share these inputs comfortably.
The Best DC to DC Chargers
We'll mostly be recommending Renogy and Victron DC to DC chargers here. Shane and I both have a Victron battery to battery charger, and we find them hard to beat on price considering the advanced feature set and 5-year warranty. Renogy have become their main competitor, beating Victron on price in exchange for warranty length, but also offering combined DC-DC/MPPT units. We also like European manufacturer NDS' variable-output charger, which gives you the flexibility to upgrade your system down the road.
Best Budget Split Charge System
If you've got a small, simple system and a tight budget, a voltage-sensing relay can't be beaten on price. It won't work with a smart alternator or lithium batteries, but delivers 60A of charging power and comes in a kit with everything you need for the installation.
Best DC to DC Charger - Budget
Renogy's DC-DC chargers offer an impressive feature set for a very low price. Both their 20A and 40A chargers offer compatibility with all battery chemistries, optimised charging profiles, fanless cooling, and a full suite of safety certifications. You sacrifice slightly on efficiency (94% compared to 98% for Victron's Orion XS range), and the 2-year warranty is shorter than Victron's 5 years. However, at this price point, and with the bundled Bluetooth module, these chargers are easy to recommend.
Best DC to DC Charger - Overall
Victron can't be beaten for feature sets and their sterling reputation is backed up by a 5-year warranty. The 50A Orion XS offers the highest efficiency rating we've seen at 98%, as well as built-in Bluetooth and seamless integration with Victron's GX monitoring ecosystem. Other than that, you get automatic, optimised charging profiles for all battery types, fanless cooling, and comprehensive safety features.
Best DC to DC Charger - Runner-up
NDS' variable-output Powerservice model is interesting because you can set it to output 40A, 60A, or 80A of power. 80A is an impressive capacity for the price, so it's worth considering as a large-capacity charger for systems that can handle it. The variable output builds flexibility into your system, allowing you to add batteries down the line without having to buy a new DC to DC charger. There's no Bluetooth, but the N-Bus plug means you can attach a display for monitoring. Besides this, we have automatic, optimised charging profiles for all battery types and comprehensive safety features.
Best DC to DC Charger with Solar Input
Renogy's 50A DC to DC charger with solar input is a good option for small campers who want to save on cost and wiring. Its built-in MPPT solar charge controller manages input from solar panels, and the DC to DC charger takes over whilst driving. Bigger systems won't get the highest possible charging speeds as combined alternator and solar input is throttled to 50A, but a combined unit is worth considering for a simpler electrical system. Built-in Bluetooth and full safety certification sweeten the deal.
Best DC to DC Charger Kit
Buying your charger in a kit means you'll have all the wiring, fuses, and lugs you need for the installation, all sized correctly. We highly recommend buying everything you can in the form of a kit, as the added peace of mind makes a big difference on a project that can otherwise feel overwhelming. Sunstore Solar offer our favourite DC to DC charger, Victron's 50A Orion XS, in a kit which includes positive and negative cable, fuse holders, fuses, and all the necessary cable lugs.
Final Thoughts
You should now feel fully equipped to choose a battery to battery charger based on your battery type, system size, and desired feature set. When you're ready, take a look at our favourite budget DC to DC charger from Renogy, or go with Victron's fully-featured Orion XS in a ready-to-install kit. If you need more information on DC to DC chargers before buying, our comprehensive guide should answer all your questions.
Don't forget to subscribe to The Van Conversion Newsletter for everything you need to get started with your own van conversion (we'll send you a free wiring diagram when you join).
If you're looking for some guidance with your van conversion, you might be interested in our book Roaming Home, or in our online course The Van Conversion Mastery Course. You'll learn directly from our founder Shane how to convert a van into your dream home - no prior experience needed. Shane also offers one-to-one consultations, where he'll help you with any aspect of your build in a face-to-face video call. All consultations come with a free copy of Roaming Home and our Diagram Pack.
Finally, our Van Conversion Ultimate Guide lays out the whole van conversion process in easy-to-follow sections with tools, materials, and step-by-step instructions. It's the perfect companion for your van build.
Until next time.
