A battery disconnect must be rated for the actual DC current and switching duty, and its position determines which circuits remain live.
A battery disconnect switch is a simple but valuable addition to any van build. Here's what you need and how to install it.
What a battery disconnect switch does
It's a high-current switch in the main positive cable between your battery and the rest of the electrical system. Throw it off:
- All 12V house loads go dead (fridge, inverter, lights, everything)
- Solar panels continue charging the battery (MPPT is still connected)
- The battery is isolated from parasitic draws during storage
This is distinct from a fuse, which only opens under overcurrent conditions. A disconnect is operator-controlled.
Types of battery disconnect switches
Manual disconnect (the standard)
A simple rotary or lever switch rated for battery current — 100A, 200A, or 300A continuous. Turn to OFF and everything cuts.
Best choices:
- Blue Sea Systems 9005e (300A): The most popular choice in the van build community. Well-built, terminal-mount, $25–35. Handles sustained current without heat buildup.
- Victron Battery Protect: Technically an electronic disconnect with low-voltage cutoff — a slightly different tool (see below).
- Perko 8500DP: Marine-grade, widely used, handles 300A continuous.
Install location: In the main positive cable, within 18 inches of the battery positive terminal. Before the fuse is fine — the disconnect is not a replacement for a fuse. Fuse the cable too.
Remote/solenoid disconnect
A heavy-duty solenoid (relay) that opens and closes the circuit via a low-current trigger wire. You wire a small switch in an accessible location that controls the solenoid — useful if your battery is buried and a manual switch is inconvenient to reach.
Products: Blue Sea Systems ML-Series Remote Battery Switches, Victron Argofet (though that's more of an isolator), generic 200A solenoids.
Best for: Builds where the battery bank is deeply built in and a manual switch isn't accessible.
Victron Battery Protect
Not exactly a disconnect switch, but a low-voltage protection device that also acts as an electronic disconnect. It monitors battery voltage and automatically disconnects loads when voltage drops below a set point (to prevent deep discharge damage), and can also be triggered manually via a remote wire.
Best for: Systems where you want automatic low-voltage protection in addition to manual control.
What a disconnect switch doesn't do
It doesn't cut power from solar panels to the battery. The MPPT controller is typically connected directly to the battery (before the disconnect). To cut solar charging, disconnect at the MPPT's PV input or battery terminals instead.
It doesn't protect against high-current faults. A fuse is still required. The disconnect is a planned, operator-initiated cutoff — not a fault protection device.
It doesn't replace a shore power isolation. If you're on shore power, the shore power charger may feed the battery on a separate circuit — a disconnect on the battery itself doesn't kill shore power input.
How to wire it
Standard wiring position:
Battery (+) → Disconnect switch → Main fuse → Positive bus bar → Loads
Some builders place the main fuse before the disconnect, others after. The key is that the fuse is within 18 inches of the battery positive terminal — its position relative to the disconnect is secondary.
Wire connections: Use the same AWG as the rest of your main cable run. If your main positive is 2/0 AWG, your connections at the disconnect are 2/0 AWG ring terminals.
Mounting: Mount the switch securely so it can't toggle from vibration. Some switches have a locking position (the Blue Sea 9005e has a removable key that prevents accidental re-connection — useful for service work).
Storage use case
For long-term van storage: charge battery to ~50%, disconnect the main disconnect switch. Parasitic draws (battery monitor, anything on standby) are eliminated. The battery sits in isolation until you return.
Worked planning check
If the inverter draws 120A and other loads draw 15A, assess at least the combined 135A operating load plus startup requirements. A switch on the load branch can leave solar connected; a battery master switch has different consequences. Draw every remaining live source before choosing its position.
The figures or dimensions in this example are explicit planning assumptions, not a product test or an installation specification. Replace them with your equipment data and actual measurements.
Planning questions
Can I choose a fuse just from the appliance current?
No. Check cable ampacity under the installed conditions, equipment instructions, terminal limits, DC voltage and interrupt capacity. Protection must coordinate with the complete circuit.
Does a wiring diagram prove the installation is safe?
No. It is a planning record. Actual routing, termination, protection and commissioning results must agree with the design and applicable requirements.
When should I involve an electrician?
Before work that exceeds your competence, particularly mains design, source transfer, bonding, high-current faults and final inspection or testing. Agree the scope and evidence of verification in advance.
Related
- Wiring & safety guide
- Bus bars for van builds explained
- Van electrical grounding guide
- Winterizing RV lithium batteries
Use the free electrical planner to organise your daily loads and charging assumptions.
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Jack Kennedy is a self-builder who has built two vans. He created Roam Wired to simplify conversion planning and share free tools, supported by affiliate links.
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