What Are Battery Isolators and Combiners?
Battery isolators and combiners are devices that manage the connection between two or more separate battery banks. They allow a single charging source (such as an alternator, solar charge controller, or battery charger) to charge multiple battery banks simultaneously while preventing the banks from discharging into each other. The result is a protected, fully charged dual-battery system where each bank remains independent during discharge.
Battery Combiners vs Battery Isolators: What Is the Difference?
Battery Combiners
A battery combiner connects two battery banks in parallel when a charging source is active. When voltage rises above a set threshold (indicating active charging), the combiner closes and allows both banks to charge together. When charging stops and voltage drops, the combiner opens and separates the banks, protecting each one from being drained by the other.
Victron Energy Cyrix battery combiners use intelligent voltage sensing to open and close automatically with no manual intervention required.
Battery Isolators
A battery isolator allows current to flow from one charging source to multiple battery banks simultaneously while preventing reverse current flow between banks. Unlike a combiner, an isolator does not connect the banks together but routes charge independently to each one using high-current diodes.
Victron Energy Argofet and Argodiode isolators use MOSFET or diode technology to eliminate the voltage drop traditionally associated with isolators, ensuring batteries receive full charging voltage from the alternator or charger.
Victron Energy Battery Isolators and Combiners at Volts Energies
All 36 products in this collection are Victron Energy units. Volts Energies is an authorized Canadian Victron Energy dealer with nationwide shipping.
Victron Energy Cyrix Battery Combiners
The Cyrix series is Victron Energy's intelligent battery combiner range. Cyrix units use microprocessor-controlled voltage sensing to combine and separate battery banks automatically. They replace traditional VSR (voltage-sensitive relay) units with faster response, lower voltage drop, and full compatibility with lithium battery systems.
Cyrix-ct (Lead-Acid Compatible): The standard Cyrix-ct intelligently connects two battery banks when the primary bank reaches a charging voltage, and disconnects them when charging stops. Available in 12/24V configurations.
Available at Volts Energies:
- Cyrix-ct 12/24V-120A
- Cyrix-ct 12/24V-230A
Cyrix-i (High Current): The Cyrix-i is built for high-current applications requiring 400A capacity at 24/48V, suited for large off-grid systems and commercial vehicle dual-battery setups.
Available at Volts Energies:
Cyrix-Li-ct (Lithium Battery Combiner): The Cyrix-Li-ct is specifically designed for systems with a lithium (Li-ion or LiFePO4) main battery bank and a standard lead-acid starter battery. It allows the lithium bank to charge the lead-acid starter battery without risk of overcharging or reverse discharge.
Available at Volts Energies:
- Cyrix-Li-ct 12/24V-120A
- Cyrix-Li-ct 12/24V-230A
Cyrix-Li-charge (Intelligent Charge Relay): The Cyrix-Li-charge protects lithium battery banks by only connecting an external charger (alternator or shore power charger) to the lithium bank when it is safe to do so. It receives an allow-to-charge signal from the Battery Management System (BMS) before closing.
Available at Volts Energies:
- Cyrix-Li-charge 12/24V-120A
- Cyrix-Li-charge 12/24V-230A
- Cyrix-Li-charge 24/48V-120A
- Cyrix-Li-charge 24/48V-230A
Cyrix-Li-load (Intelligent Load Relay): The Cyrix-Li-load disconnects loads from a lithium battery bank when the BMS signals a low-state-of-charge condition, protecting lithium cells from deep discharge damage.
Available at Volts Energies:
- Cyrix-Li-load 12/24V-230A
- Cyrix-Li-load 24/48V-230A
Victron Energy Argofet Battery Isolators
The Argofet series uses MOSFET technology to eliminate the voltage drop of traditional diode isolators. Conventional diode isolators cause a 0.6V drop that results in undercharged batteries. Argofet MOSFETs reduce this drop to near zero, ensuring batteries receive full alternator or charger voltage.
Available at Volts Energies:
- Argofet 100-2 Two batteries 100A
- Argofet 100-3 Three batteries 100A
- Argofet 200-2 Two batteries 200A
- Argofet 200-3 Three batteries 200A
Victron Energy Argodiode Battery Isolators
The Argodiode series uses standard Schottky diodes for battery isolation. A cost-effective choice for systems where a small voltage drop is acceptable and simplicity is the priority.
Available at Volts Energies:
- Argodiode 80-2SC 2 batteries 80A
- Argodiode 140-3AC 3 batteries 140A
Victron Energy BCD Combiner Diodes
The BCD (Battery Combiner Diode) series combines battery isolation diode technology with low cost for basic two-battery setups. Suitable for smaller vehicles and marine applications requiring simple dual-battery management.
Available at Volts Energies:
- BCD 402 2 batteries 40A
- BCD 802 2 batteries 80A
How to Choose the Right Battery Isolator or Combiner
Do you have two standard lead-acid battery banks? Choose a Victron Cyrix-ct combiner (120A or 230A). It automatically combines the banks during charging and separates them at rest.
Do you have a lithium main battery and a lead-acid starter battery? Choose a Victron Cyrix-Li-ct. It safely connects the lithium bank to charge the starter battery without risking overcharge or reverse discharge.
Do you need BMS-controlled charge or load protection for a lithium system? Choose a Cyrix-Li-charge (for charge protection) or a Cyrix-Li-load (for load disconnect protection). Both respond to allow-to-charge and allow-to-discharge signals from your Battery Management System.
Do you need to charge three battery banks from one alternator or charger? Choose an Argofet 100-3 or Argofet 200-3. The three-output Argofet routes charge to three independent battery banks simultaneously with virtually no voltage drop.
Do you need 400A capacity for a large commercial or off-grid system? Choose the Cyrix-i 24/48V-400A for high-current dual-battery combining at 24V or 48V system voltage.
Current Rating Guide
Selecting the correct amperage rating for your combiner or isolator is critical for safe operation. The current rating should always meet or exceed your system's maximum charging current.
- Small Vehicle Alternator (40A–80A): Choose an 80A–120A rated combiner or isolator.
- Standard Alternator (80A–120A): Choose a 120A–140A rated model.
- High-Output Alternator (120A–200A): Use a 200A–230A rated unit.
- Large Off-Grid Charger or Inverter Charger (200A+): Select a 230A–400A rated model.
Tip: Always choose the next higher current rating to handle temporary peak current spikes safely.
System Voltage Guide
Your battery system voltage determines which Cyrix model is compatible with your installation.
For 12V Battery Systems
Compatible models include:
- Cyrix-ct 12/24V
- Cyrix-Li-ct 12/24V
- Cyrix-Li-charge 12/24V
For 24V Battery Systems
Compatible models include:
- Cyrix-ct 12/24V
- Cyrix-i 24/48V
- Cyrix-Li-charge 24/48V
For 48V Battery Systems
Compatible models include:
- Cyrix-i 24/48V
- Cyrix-Li-charge 24/48V
- Cyrix-Li-load 24/48V
Compatible Products at Volts Energies
Battery isolators and combiners integrate directly with the following products available at Volts Energies:
- LiFePO4 Batteries, pair Cyrix-Li-ct or Cyrix-Li-charge with Pylontech and other lithium banks
- AGM Batteries, pair Cyrix-ct or Argofet with lead-acid battery banks
- Battery Management Systems, required for Cyrix-Li-charge and Cyrix-Li-load operation
- Battery Monitors, monitor both battery banks with Victron SmartShunt or BMV
- Battery Relays, for additional switching and load control
- Inverter Chargers, MultiPlus units used as the primary charging source for dual-bank systems
- Battery Chargers, shore power chargers for marina and stationary dual-bank systems
- DC Distribution Systems, busbars and fusing for dual-bank wiring
FAQs
What Is The Difference Between A Battery Combiner And A Battery Isolator?
A combiner connects two battery banks in parallel during charging and separates them at rest. An isolator allows one charging source to charge two banks simultaneously without connecting the banks to each other at any time. Combiners are simpler and more efficient. Isolators are preferred when banks must remain fully independent at all times.
Will A Victron Cyrix Combiner Work With My Lithium Lifepo4 Battery?
Standard Cyrix-ct models are designed for lead-acid battery voltage profiles and are not recommended for direct use as a lithium combiner. For lithium systems, choose the Cyrix-Li-ct, Cyrix-Li-charge, or Cyrix-Li-load, which are specifically engineered to work with BMS-controlled lithium battery banks.
What Is The Voltage Drop On An Argofet Isolator?
The Argofet uses MOSFET technology to reduce voltage drop to near zero. Traditional diode isolators cause a 0.6V drop that results in undercharged batteries over time. The Argofet eliminates this problem, making it the preferred isolator for systems where full battery charge is critical.
Can I Use A Battery Combiner With Solar Charging?
Yes. A Cyrix combiner can be used in systems where a solar charge controller is the primary charging source. When the controller raises battery voltage during the absorption phase, the Cyrix closes and begins charging the secondary bank. When charging ends and voltage drops, the Cyrix opens and protects both banks.
Does Volts Energies Ship Battery Isolators And Combiners Across Canada?
Yes. All battery isolators and combiners ship nationwide across Canada. Free shipping applies on orders over $297.
Do I Need A Battery Management System (BMS) To Use The Cyrix-Li-Charge?
Yes. The Cyrix-Li-Charge requires an allow-to-charge signal from a BMS to operate. Without a BMS providing this signal, the relay will not close. It is designed to work within a fully managed lithium battery system.
