Updated: 23 September 2026 · EuroVan Shop
In short: A DC to DC charger charges your leisure battery from the alternator with a proper charge profile and a limited current, so it suits lithium batteries and modern vans. A split charge relay simply connects the two batteries while the engine runs. For a LiFePO4 battery, choose a DC to DC charger such as the Victron Orion-Tr Smart 12/12-30A, included in our VANPOWER kit.
See the VANPOWER electrical kitWhat does a DC to DC charger do?
A DC to DC charger takes power from the starter battery and alternator while you drive and turns it into a controlled charge for your leisure battery. It is a charger in its own right: it sets its own output voltage and current, whatever the alternator is doing, and follows a charge profile chosen for your battery type.
The Victron Orion-Tr Smart 12/12-30A delivers up to 30 A continuous (40 A peak), switches on only when it detects that the engine is running, and charges in three stages: bulk, absorption and float. It works with AGM, GEL and lithium leisure batteries, and you set it up and monitor it over Bluetooth in the VictronConnect app.
It is the alternator charger in our VANPOWER electrical kit, alongside solar and hook-up charging. Browse the whole campervan electrical system range to see every part sold separately.
Victron Orion-Tr Smart 12/12-30A
DC to DC charger: 30 A (40 A peak), engine-running detection, 3-stage charge, Bluetooth.
VANPOWER kit
LiFePO4 battery + Orion-Tr Smart + SmartSolar MPPT + hook-up charging, with wiring diagram.
How does a split charge relay work?
A split charge relay is an automatic switch between the starter battery and the leisure battery. When the engine runs, it closes and connects the two batteries, so the alternator charges both. When the engine stops, it opens again, and the leisure battery can no longer drain the starter battery.
A relay is triggered either by the ignition or by sensing the voltage rise when the alternator starts charging (a voltage-sensing relay, often called a VSR). Either way, the relay does not charge anything itself. The leisure battery simply receives whatever voltage the alternator and the wiring deliver, with no charge profile and no current limit.
That simplicity is why split charge was the standard set-up in campervans for years, and a relay can still do the job in an older van with a lead-acid leisure battery. EuroVan Shop does not sell split charge relays; we explain them here so you can compare fairly.
DC to DC charger vs split charge relay: side-by-side comparison
A DC to DC charger controls the charge; a split charge relay only connects the batteries. Everything else follows from that difference.
| Criterion | DC to DC charger | Split charge relay |
|---|---|---|
| How it charges | Regulated output with a charge profile (Orion-Tr Smart: bulk, absorption, float) | Direct connection: the leisure battery gets the alternator voltage |
| Charging current | Limited to the charger rating (Orion-Tr Smart: 30 A, 40 A peak) | Not limited by the relay; depends on alternator, cables and battery |
| Lithium (LiFePO4) leisure battery | Suitable, with a lithium charge profile | Not recommended: no lithium profile, no current limit |
| Alternators with varying voltage | Output voltage set by the charger | Passes on whatever voltage the alternator delivers |
| Starter battery protection | Engine-running detection: off when parked | Opens when the engine stops |
| Monitoring | Bluetooth, VictronConnect app (Orion-Tr Smart) | Usually none |
| Installation | Charger with fused input and output cables | Relay with fused cables, the simplest set-up |
Do you really need a DC to DC charger?
You need a DC to DC charger if your leisure battery is lithium, if your van has a smart alternator, or if you want the battery properly full after a drive. A split charge relay can be enough in an older van with a lead-acid leisure battery and a short cable run.
- Lithium leisure battery: it needs its own charge profile and a controlled current (see below).
- Smart alternator: many recent vans use alternators whose voltage varies with driving conditions. A relay passes that variation straight to the leisure battery; a DC to DC charger sets its own output.
- Long cable run: the leisure battery often sits at the back of the van, several metres from the starter battery. Voltage lost in the cable lowers the charging voltage with a relay; a DC to DC charger compensates by regulating its output.
- A full battery: the 3-stage charge brings the battery to full, then holds it at float.
If you move often and camp off grid, the alternator is an important charging source, especially in winter when solar gives less. That is where a DC to DC charger makes the most difference.
Will a DC to DC charger drain my starter battery?
No. The Victron Orion-Tr Smart switches on only when it detects that the engine is running, so it never draws down your starter battery while you are parked.
As soon as the alternator is charging, the charger starts; when you switch off the engine, it stops. Your leisure battery can then run the fridge, lights and water pump all night without touching the battery you need to start the van in the morning.
For extra peace of mind, fit a battery isolator switch on the circuit so you can cut it completely during a long lay-up or while you work on the system. More on that below.
Do you need a DC to DC charger for a lithium battery?
Yes. For a lithium (LiFePO4) leisure battery, a DC to DC charger is the right choice, and it is what we fit in every VANPOWER kit.
A LiFePO4 battery can accept a high charge current. Connected straight to the alternator through a relay, it can draw as much as the alternator and cables allow, for as long as the engine runs. A DC to DC charger caps that current at its rating (30 A for the Orion-Tr Smart) and applies a lithium charge profile.
Our LiFePO4 lithium battery (12.8 V, 100, 200 or 314 Ah) has a built-in BMS against overcharge, short circuit and deep discharge, and is designed to work with Victron charging equipment. Its BMS pauses charging below 0 °C to protect the cells, which is normal for any LiFePO4 battery: in freezing weather, charging resumes once the battery is above 0 °C. Comparing chemistries? Read LiFePO4 vs AGM batteries.
LiFePO4 lithium battery
12.8 V, 100 / 200 / 314 Ah, built-in BMS, up to 6000 cycles, Bluetooth.
Victron Orion-Tr Smart 12/12-30A
Lithium, AGM and GEL profiles; several units can be paralleled.
What size DC to DC charger for a 100Ah lithium battery?
A 30 A DC to DC charger such as the Victron Orion-Tr Smart 12/12-30A is a good match for a 100 Ah lithium battery, and it is the charger we supply with every VANPOWER battery size (100, 200 and 314 Ah).
At full output, 30 A puts back up to about 30 Ah per hour of driving. Output power is 430 W at 25 °C and 360 W at 40 °C, so expect a little less on a hot day. The table gives rough estimates to recharge from about 20% to full by driving alone, with nothing else running.
| Battery | Charge to put back (estimate, 20% to 100%) | Driving time with one 30 A charger (estimate) |
|---|---|---|
| 100 Ah | about 80 Ah | about 3 hours |
| 200 Ah | about 160 Ah | about 5 to 6 hours |
| 314 Ah | about 250 Ah | about 8 to 9 hours |
These are estimates: they ignore the slower absorption stage at the end of the charge and any power used while you drive. Most trips combine driving with solar and the odd night on hook-up, so the charger rarely does the whole job alone.
If you drive little and want faster alternator charging for a large battery, several Orion-Tr Smart units can be connected in parallel. Ask our team first: the alternator and wiring must be able to supply the extra current.
See the Orion-Tr Smart 12/12-30A
Do you need a battery isolator with a DC to DC charger?
You do not need a separate split charge isolator, because the DC to DC charger already stops when the engine is off. A manual battery isolator switch on each circuit is still good practice for safety and maintenance.
In the VANPOWER kit, the battery isolator switch is used three times: on the battery, solar and alternator circuits. Each one lets you cut a circuit completely, for example to lay up the van for the winter, replace a component or trace a fault. The switch is rated 12 to 48 V and 275 A continuous (455 A intermittent), with tinned copper M10 studs.
Isolators do not replace fuses. Every positive cable leaving a battery needs a fuse as close to that battery as possible, on the starter battery side and the leisure battery side of the DC to DC charger. The ratings depend on the cable sections and are given in the VANPOWER wiring diagram; if you design your own system, have them sized by a qualified person.
Battery isolator switch 275 A
12 to 48 V, 275 A continuous, M10 studs. Used on each circuit of the VANPOWER kit.
Terminal lugs and fuses pack
Terminal lugs, MEGA fuses and resettable fuses for the VANPOWER kit.
Where is a DC to DC charger connected?
A DC to DC charger sits between the starter battery (its input) and the leisure battery (its output), with a fuse close to each battery.
- Input: from the starter battery and alternator circuit, fused close to the starter battery.
- Output: to the leisure battery or its bus bar, fused close to the leisure battery.
- Location: somewhere dry and ventilated, usually near the leisure battery so the output cable stays short.
The VANPOWER kit comes with a detailed wiring diagram (with cable sections) and a step-by-step tutorial, and our team gives free technical support while you install it. Our 12 V campervan wiring diagram guide shows where each part goes. For approval of your conversion, check your national rules (DVLA/VCA, TÜV, RDW); the kit components are ECE R10 certified.
How a DC to DC charger works with solar and hook-up
The DC to DC charger is one of three charging sources in a complete campervan system: the alternator while driving, solar when parked, and mains on hook-up.
In the VANPOWER kit, the Victron Orion-Tr Smart handles the alternator, a Victron SmartSolar MPPT 100/30 handles 300 to 500 W of solar panels, and hook-up charging comes from a Victron Blue Smart IP22 15 A charger or, if you choose an inverter, from its built-in 20 A charger. All three charge the same LiFePO4 battery, and the Victron parts are monitored over Bluetooth in the VictronConnect app.
Planning solar too? Read how many solar panels you need on a campervan, or start with our campervan electrical system guide.
Not sure how to size your 12 V system?
Send us your appliances and how you travel (weekends, several days, full time). Our France-based technical team answers within 24 hours and can build a custom kit.
Ask our technical teamFrequently asked questions
Is a DC to DC charger better than a split charge relay?
For a lithium leisure battery or a van with a smart alternator, yes: it applies a charge profile and limits the current. A split charge relay only connects the batteries while the engine runs, which can be enough for an older van with a lead-acid leisure battery.
Will a DC to DC charger drain my starter battery?
No. The Victron Orion-Tr Smart has engine-running detection: it switches on only when the alternator is charging and stops when you switch off the engine.
Can I use a split charge relay with a lithium leisure battery?
It is not recommended. A relay gives no lithium charge profile and no current limit, so a LiFePO4 battery can draw as much as the alternator and cables allow. Use a DC to DC charger instead.
What size DC to DC charger do I need for a 100Ah lithium battery?
A 30 A charger such as the Victron Orion-Tr Smart 12/12-30A. As a rough estimate, it puts back up to about 30 Ah per hour of driving at full output.
Can the Orion-Tr Smart charge an AGM battery?
Yes. It charges AGM, GEL and lithium leisure batteries with a 3-stage bulk, absorption and float charge, set up in the VictronConnect app.
Do I need a battery isolator with a DC to DC charger?
Not to protect the starter battery, as the charger stops when the engine is off. A manual isolator switch on each circuit, plus fuses close to each battery, is still good practice for safety and maintenance.
Want alternator, solar and hook-up charging in one pre-sized system, with the wiring diagram?
See the VANPOWER kit
