How to Wire a Leisure Battery in a Campervan

Wiring a leisure battery into a campervan correctly is the foundation everything else depends on. Get this wrong and the whole system is compromised. Get it right and the rest of the wiring follows naturally.

The basic connection sequence

The leisure battery is the centre of your 12V system. Everything connects through it:

• Charge sources (solar MPPT, DC-DC charger, mains charger) connect to the battery to charge it
• Loads (fridge, lights, inverter) draw from the battery
• A battery monitor (shunt) sits in the circuit to track current in and out

Main positive cable

The main positive cable runs from the battery positive terminal → ANL fuse holder → main positive bus bar.

Fuse placement: The ANL fuse must be within 300mm of the battery positive terminal. This is the critical safety requirement — a fault anywhere in the positive cable downstream of the fuse causes the fuse to blow, not the cable to catch fire.

Cable size: Size based on your total system load. For most builds with an inverter:

• 1,000W inverter: 25mm² main positive
• 2,000W inverter: 50mm² main positive
• 3,000W (MultiPlus): 70mm² main positive

The main cable must handle the maximum combined current draw of all loads that might run simultaneously.

Main negative cable

The main negative cable runs from the battery negative terminal → main negative bus bar (and/or chassis earth point).

In a standard van conversion, the negative system uses the van's metal body as the return path (negative earth system). The battery negative connects to both:

1. A negative bus bar (for direct negative connections from loads)
2. A chassis earth point (bare metal of the van body)

All 12V loads connect their negative to either the bus bar or directly to nearby chassis earth points. The chassis conducts the current back to the battery negative.

Cable size: Match the negative cable size to the positive cable size.

Bus bars

A bus bar is a copper or aluminium block with multiple connection points. It provides a clean, organised way to connect multiple cables to the same point.

Positive bus bar: Takes the main positive cable from the ANL fuse and distributes to individual circuits (MPPT output, DC-DC charger output, fuse box input, inverter input).

Negative bus bar: Connects all load negatives together and to the battery negative/chassis.

Alternative: Many builders use a combined distribution block (Anderson Power Products, Victron, or similar) that integrates both positive and negative buses with individual fuses for each circuit.

Battery monitor (shunt) placement

A coulomb-counting battery monitor (Victron BMV-712, SmartShunt) uses a shunt — a precision resistor — to measure all current flowing in and out of the battery.

For accurate monitoring, the shunt must be in the main negative cable, between the battery negative terminal and everything else — the only connection between battery negative and the rest of the system must pass through the shunt.

Shunt placement:

• Battery negative terminal → shunt → main negative bus bar (and chassis earth)
• No direct battery negative bypass connections — all negatives must go via the shunt

If any load or charge source bypasses the shunt (connecting directly to battery negative without going through it), the monitor will not account for that current and will give inaccurate readings.

Leisure battery to starter battery isolation

The leisure battery and starter battery must be electrically separate during normal use — you do not want to accidentally flatten the starter battery using leisure loads.

They connect via a charge source (DC-DC charger or relay) that controls when current flows between them. The DC-DC charger:

• Only operates when the engine is running
• Charges the leisure battery from the alternator
• Prevents leisure loads from draining the starter battery

Do not connect leisure and starter batteries directly in permanent parallel.

Example wiring sequence for a single leisure battery

1. Battery in its enclosure with positive and negative terminal covers on
2. Negative cable: battery negative → shunt → negative bus bar → chassis earth point
3. Positive cable: battery positive → ANL fuse holder (fuse not yet inserted) → positive bus bar
4. Connect all charge sources to bus bars: MPPT output positive to positive bus bar, MPPT output negative to negative bus bar (upstream side of shunt)
5. Connect DC-DC charger: output positive to positive bus bar, output negative to negative bus bar
6. Connect fuse box: inline fuse or MCB from positive bus bar; negative to negative bus bar
7. Connect inverter: dedicated cable with its own ANL fuse from positive bus bar; negative from negative bus bar
8. Insert main ANL fuse last, once all connections are complete and checked

FAQ

Should my leisure battery be connected to the chassis (earthed to the van body)?

The negative terminal should be earthed — but through a defined connection point, not via the battery mounting brackets. Run a dedicated negative cable from the negative terminal (or negative bus bar) to a clean chassis point.

Do I need a battery isolator switch?

A main isolator switch (e.g., on the positive cable between battery and ANL fuse, or downstream of the ANL fuse) is good practice — it lets you disconnect the system quickly for maintenance. Many builds use a large rotary isolator switch in an accessible position.

My leisure battery positive is connected directly to my fridge with no bus bar. Is that OK?

It works, but for anything beyond one load, a bus bar is much cleaner. A single fridge connected directly to the battery is fine as long as it has its own inline fuse. As you add more loads, a bus bar avoids multiple cables at the battery terminal.