The Cyrix-Li-charge 12/24V-230A is a microprocessor-controlled charge relay from Victron Energy that combines a lithium (LiFePO4) service battery with a lead-acid starter battery in 12V or 24V systems. It lets an alternator or charger feed both banks at once, while keeping the lithium battery protected from unsafe charging conditions. It suits marine, vehicle and off-grid setups pairing a lithium service bank with a conventional starter battery.

Key features of this battery isolator switch

• Current rating, 230A continuous, for 12V or 24V systems.
• Control, microprocessor controlled, monitors voltage on both banks and connects them only when charging conditions are safe.
• BMS interface, opens immediately on a charge-disconnect signal from the lithium BMS, within milliseconds.
• Auto-disconnect, opens when charging stops, so the starter battery cannot be drained by the lithium bank.
• Voltage detection, works on 12V or 24V without manual configuration.
• Weight, 0.3 kg.

How it works

The relay sits between the lithium service battery and the starter battery. When the alternator or an external charger raises voltage on the starter battery side above the connection threshold, the relay closes and charge current flows into the lithium bank too. When charging stops and voltage drops, the relay opens again, isolating the two banks so the lithium battery cannot back-feed the starter battery.

Unlike a standard Cyrix-ct relay, this unit takes a direct input from the lithium BMS. If the BMS signals an overvoltage or temperature fault and calls for a charge stop, the relay opens within milliseconds regardless of bus voltage. This BMS connection is a required part of a safe lithium installation, not an optional extra. At 230A the relay handles the output of most marine and vehicle alternators without derating.

Applications

• Marine vessels with a lithium service bank and a separate lead-acid start battery charged from the alternator.
• Motorhomes and campervans running a lithium leisure battery alongside the vehicle starter battery.
• Off-grid and expedition vehicles where alternator charging feeds a lithium house bank.
• Any 12V or 24V dual-battery setup needing automatic, safe charge sharing between lithium and lead-acid banks.

What's in the box

• 1x Victron Cyrix-Li-charge 12/24V-230A intelligent charge relay

Installation notes

Fit by a qualified electrician or experienced marine/vehicle installer. The BMS charge-disconnect output must be wired to the Cyrix-Li-charge control input for correct and safe lithium operation. Leaving this connection out removes the main protection for the lithium battery.