Battery Isolators
Marine Battery Isolators & Split Charge Systems
Protect your vessel's electrical system and ensure reliable starting power with professional battery isolation solutions. Our collection includes:
- Split Charge Diodes - Simple, reliable battery isolation
- Split Charge Relays - Voltage-sensitive relay (VSR) systems
Battery isolators prevent house battery discharge from affecting engine starting batteries, essential for safe operation. Modern VSR systems automatically connect batteries during charging and isolate them when the engine stops.
Complete Charging System: Use with marine batteries, battery chargers, alternators and regulators. Monitor with battery monitoring from Victron Energy or Mastervolt. Distribute power via DC distribution systems.
Diode or relay: choosing a split charge method
Split charge diodes and voltage-sensitive relays solve the same problem in different ways. A diode isolator has no moving parts and fails safe, but it introduces a small voltage drop across the diode, typically around 0.5V, which can leave a battery slightly undercharged unless the alternator's regulator compensates for it. A VSR relay avoids that drop entirely by physically switching the batteries together once charging voltage is detected, but it needs to be sized to the alternator's full output current and wired so it can sense voltage correctly on both sides.
Either device needs to be rated above the alternator's maximum output, not just its typical output, and protected with a fuse sized to the cable it is wired with. Where a system includes a lithium bank, check the isolator or relay suits the charging profile lithium batteries expect, since some VSR designs assume a lead acid absorption curve. Pair either method with proper battery monitoring so you can see how the banks are actually charging, rather than assuming the isolator is doing its job.
