Blue Sea Systems m-Series Mini On-Off Battery Switch with Key, Red

The Blue Sea Systems m-Series Mini On-Off Battery Switch is the simplest way to fully disconnect a battery from its load — a single switch position for On, a single position for Off, with no selector complexity in between. It's the standard choice for disconnecting a battery bank when the boat sits unused, during service work, or in an emergency shutdown situation.

Key features

• 300A continuous, 500A intermittent (5 min), 1500A cranking (10 sec)
• 48V DC maximum, 3/8" (M10) tin-plated copper studs
• Ignition protected, IP66 rated, one-piece stud design never loosens
• Case design allows surface, front-panel, or rear-panel mounting

Because it's a true mechanical disconnect rather than an electronic relay, this switch keeps working even if the boat's electrical system is otherwise dead — a reliable way to isolate a battery bank for storage, service, or safety without relying on any other component staying powered. That mechanical simplicity is also what makes it easy to inspect and service years down the line.

Torque the terminal studs to 120 in-lb (13.56 Nm). Unlike the knob version, this switch uses a removable key rather than a knob, adding a layer of security since the boat can't be started or powered up without the key present. A spare key is available separately as PN 7900. Mount it somewhere accessible enough to reach quickly in an emergency, since a fast, confident disconnect is the entire point of this switch. Check the connection periodically for tightness and corrosion, since a loose or corroded main disconnect defeats its purpose right when it's needed most — a quick visual and torque check at each haul-out is good practice.