Battery Switches
Marine Battery Switches, VSRs & ACRs - Automatic Battery Isolation
Battery switches and voltage-sensitive relay (VSR) systems for isolating, connecting and protecting battery banks. The collection covers manual and remote-operated battery switches, automatic charging relays (ACRs) and intelligent split charge relays that connect batteries during charging and isolate them when the engine stops.
Relay-based systems provide more efficient charging than diodes with minimal voltage drop, automatically managing multiple battery banks without manual intervention. Remote battery switches add safe, high-current isolation you can operate from the helm. Essential for modern marine electrical systems.
Advanced Battery Isolation: Part of our Battery Isolators collection. Compare with split charge diodes for simpler systems. Use with AGM or lithium batteries. Pair with chargers, alternators, and battery monitors.
VSR, diode or DC-DC: what to fit
A voltage-sensitive relay connects a second battery bank to the alternator once starting voltage reaches a set threshold, and drops it again when the engine stops, all with negligible voltage drop compared with an older split charge diode. That makes it a reasonable choice for a second lead-acid or AGM bank on a straightforward single-alternator boat.
Where lithium batteries are involved, a VSR alone is often not enough, since lithium can accept charge current the alternator was never designed to sustain; a DC-DC converter or dedicated lithium charging profile usually needs to sit in that circuit instead. Wiring position also matters: the relay needs to sit close to the batteries it is switching, with cable sized to the alternator's maximum output and fused at both ends, not just downstream of the relay.
