12V & 24V Battery Isolators in Perth

Without an isolator, an auxiliary battery drains the crank battery when the vehicle is off — the fridge kills the starter overnight. A voltage-sensing isolator watches the alternator voltage, connects the two batteries when the engine is running so both charge, and disconnects them as soon as it stops. Simple, cheap and non-negotiable on any dual-battery build.

A basic isolator is fine when the crank and auxiliary are the same chemistry — both AGM, sitting side by side, on an older alternator that holds 14V. As soon as you add a smart alternator, a lithium auxiliary, or a long cable run to a rear canopy, you need a proper [DC-DC charger](/collections/dc-chargers-managers) instead. The two do different jobs.

The Redarc SBI12 100A is the touring standard — small, sealed, five-year warranty, dead reliable. The SBI12D adds dual sensing so it works with solar or a second alternator. SBI212 steps to 200A for high-draw setups, and the 24V SBI224 covers trucks and heavy vehicles. There's a dedicated lithium load-disconnect variant for lithium banks that need protection from over-discharge.

For competition vehicles, mine-spec 4WDs and workshop use, a manual battery master switch is either a requirement or just good practice. We stock 200A rated master switches, pin-locator kill switches, and heavy-duty 100A continuous-duty solenoids for permanent installs. Add the mounting bracket from the same page and it's a tidy job.

A poorly installed isolator or master switch is a fire waiting to happen — the cable, the fuse and the mounting all have to be right for the current. We fit isolators, master switches and complete dual-battery setups at our Bayswater workshop, and we stock the [SBI12 installation kits](/collections/isolators) that make the wiring loom job clean. Book it in and we'll do it properly.