The Victron Cyrix-i is a microprocessor-controlled battery combiner that connects two battery banks in parallel while both are being charged, then separates them once charging stops. It suits marine, vehicle and off-grid systems where a starter battery must stay isolated from a service battery while both charge from the same source.

Key features

• Current rating, 400A continuous, for high-demand 12V and 24V systems
• Switching logic, microprocessor-controlled, connects banks only when a charge source is detected
• Operation, automatic, no manual intervention once installed
• Compatibility, lead-acid chemistries including AGM, gel and flooded
• Weight, 0.9 kg
• Voltage, works across 12V and 24V systems without reconfiguration

How it works

The Cyrix-i monitors the voltage of both battery banks continuously. When voltage on either bank rises above a set threshold, indicating an active charge source such as an alternator or shore power charger, the unit connects the banks so they charge together. Once voltage drops back below that threshold, the banks separate again, keeping the starter battery ready to crank the engine regardless of how far the service bank has been discharged.

Rather than a simple relay or diode isolator, the Cyrix-i applies time delays and hysteresis to its switching decisions. This stops rapid cycling from voltage fluctuations and avoids connecting a discharged bank to a healthy one at the wrong moment. Rated at 400A, it can carry the full output of most vehicle alternators and battery chargers without restricting the charging circuit.

It wires directly between the positive terminals of the two battery banks, needs no external control signal, and draws negligible standby current. That makes it suitable for systems that sit unused for long stretches between uses.

Applications

Marine vessels with separate starter and service banks on one alternator; motorhomes and campervans needing isolation between starter and leisure batteries; commercial vehicles with auxiliary power that must not risk engine starting; off-grid cabins with two banks on one charger or solar system; agricultural and plant machinery with dual-battery setups.

Installation notes

Fitting should be done by a qualified electrician or marine electrical engineer familiar with high-current DC systems, using correctly rated cable and fusing on each bank. Both banks need a common negative before installation. The unit is not suitable for lithium chemistries unless the battery management system is confirmed compatible with voltage-based combiners.

What's in the box

• 1 x Victron Cyrix-i 12/24V 400A intelligent battery combiner