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NCC Trained · Victron Dealer
A regulated charger between your start battery and your leisure battery — built for smart alternators and lithium, and pre-loomed by our team so the install is hours, not weekends.
Shop DC-DC charger kits Design your full system
A DC-DC charger (also called a B2B or battery-to-battery charger) charges your leisure battery from the alternator while driving. Unlike a basic split charge relay, it regulates voltage, supports lithium profiles and works with modern smart alternators. Victron's Orion XS is the market benchmark.
It depends on your van and your battery.
If your van has a classic alternator and an AGM leisure battery, a basic relay does the job — it connects the batteries together while the engine runs. Our split charge relay kits cover that route.
If your van is Euro 6 or newer, it almost certainly has a smart alternator. Smart alternators drop their output voltage to save fuel, often below the voltage a leisure battery needs to actually charge. A relay still connects the batteries — but the leisure battery barely charges. That's the gap a DC-DC charger fills: it takes whatever the alternator gives and produces a proper, regulated charge.
And if you run lithium, a DC-DC charger isn't optional — lithium batteries need regulated charging with the correct profile, not raw alternator voltage.
| Charger | Output | Lithium profile | Smart alternators | Bluetooth | From |
|---|---|---|---|---|---|
| Victron Orion XS 70A | 70A | Yes | Yes | Yes | £346.56 |
| Victron Orion XS 50A | 50A | Yes | Yes | Yes | £288.00 |
| Victron Orion Smart 30A (non-isolated) | 30A | Yes | Yes | Yes | £176.90 |
| Victron Orion Smart 18A (isolated) | 18A | Yes | Yes | Yes | £135.96 |
| Basic VSR relay kit | Pass-through | No | No | No | See kit options |
Prices render live from the shop.
Since Euro 6, van makers tune alternators to charge only when it helps fuel economy. The alternator might sit at 12-13V on the move — healthy for the start battery's purposes, below what a leisure battery needs. A relay can't change that; it just passes the voltage through.
A DC-DC charger acts like a proper mains charger running off your engine: it takes whatever the alternator provides and converts it to a regulated, temperature-compensated charge that suits the leisure battery.
Not sure if your van has a smart alternator? The test takes ten minutes with a multimeter — our split charge hub walks through it.
Match the charger to your battery bank and your driving:
Worked example: a 100Ah lithium battery used down to half needs about 50Ah back. At 50A of charging, that's roughly an hour of driving. The same battery behind a 30A charger needs over three.
Bigger is not automatically better: the charger can only feed what the battery can accept, and the alternator has to have headroom. If in doubt, the System Builder sizes it as part of the whole electrical system.
A DC-DC charger install is the work of a few hours to a day — the variable isn't the charger, it's how much of the van you have to take apart to run the cable from the main battery to the charger.
That's also where installs go wrong. The two most common mistakes are incorrect cable sizes and not using the right type or amperage of fuse. Both are quiet failures: the system works until it doesn't, and by then it's an electrical fault to trace rather than a connector to re-crimp.
Our pre-loomed DC-DC kits exist to remove exactly that risk: you're guaranteed the right cable, fuses and connectors in the right places, with professional quality joints throughout. If you're confident specifying your own cable and fuse sizes, the bare units are there for you. If you'd rather bolt in a kit and know it's right first time, that's the loom route.
Charging from mains instead? See our leisure battery chargers guide. Building a full system? The complete systems route puts the DC-DC charger in context with the rest of your electrics.
Yes — B2B (battery-to-battery), DC-DC charger and aux battery charger all describe the same thing: a charger that sits between your start battery and your leisure battery and charges the second from the first while the engine runs.
Yes — that's one of its main jobs. It takes the alternator's variable, often low output and converts it to a regulated charge voltage. A basic relay cannot do this.
Match it to your battery bank and driving pattern: 18/30A for smaller setups, 50A as the all-rounder for most builds, 70A for large lithium banks or short drives. The System Builder sizes it as part of your whole system.
Yes. The Orion XS carries a dedicated lithium charge profile and lets you set the charge parameters in the VictronConnect app.
Classic alternator and AGM battery: a relay kit is the simpler, cheaper route and works well. Smart alternator or lithium: use a DC-DC charger. If you're unsure which alternator you have, the smart-alternator test in our split charge guide settles it in ten minutes.
