Victron Argo FET Isolators: Low-Loss Multi-Bank Charging

This Victron Argo FET battery isolators review covers the Argofet range. These let one alternator or one single-output charger charge two or three batteries at once, without connecting the batteries together. Draining the house battery won’t drain the starter battery. Unlike traditional diode isolators, Argofets use FET switches, so the voltage loss is tiny. Victron rates it below 0.02V at low current and about 0.1V at higher current.

Electrical work can be dangerous: follow the manual, fuse and size every cable correctly, and use a licensed electrician for anything connected to household wiring.

Victron Argo FET Battery Isolators Review: Specs

Model	Max charge current	Max alternator current	Batteries
Argofet 100-2	100A	100A	2
Argofet 100-3	100A	100A	3
Argofet 200-2	200A	200A	2
Argofet 200-3	200A	200A	3

Source: Victron Argofet Battery Isolators with alternator energize input datasheet.

Shared specs: 12V and 24V systems, M8 bolt connections, 1.4kg, 65 x 120 x 200mm.

Shared specs: 12V and 24V systems, M8 bolts, 1.4kg, 65 x 120 x 200mm. Victron rates the voltage loss below 0.02V at low current and about 0.1V at higher current.

What We Like

Almost no voltage loss. A diode isolator drops much more, which often means raising the alternator voltage. Victron says that’s not needed with an Argofet.
Alternator energize input. Some alternators need voltage on B+ before they start charging. An isolator blocks that return voltage, so the Argofet has a current-limited energize input. It powers B+ when the engine run switch is closed.
Simple and passive. No settings and no app. It suits boats with an outboard or inboard and two or three battery banks of the same type.
Three-output versions for a starter, a house bank and a thruster or windlass battery.

What to Watch

It does not change voltage. Each battery gets roughly the alternator’s own voltage. If your batteries need different charge voltages, such as lithium house and lead-acid starter, or if you have a smart alternator, a DC-DC charger like the Orion XS fits better.
Cable sizing still matters. Victron’s own example: 100A through 10m of 50mm² (AWG 0) cable drops 0.26V. 50A through 5m of 10mm² (AWG 7) drops 0.35V. Keep runs short and thick.
No current limiting. A large lithium bank can pull as much as the alternator will supply. Size the isolator to the full alternator output.

Argo FET vs DC-DC Charger

Choose an Argofet for same-chemistry lead-acid banks on a conventional alternator, especially on boats with multiple banks. Choose an Orion XS or Orion-Tr Smart for lithium house banks, smart alternators, or when you need a set charge profile and current limit.

Setup: There Isn’t Much

The Argofet has no app and no settings. The setup decisions are wiring choices:

Size it to the alternator. Pick 100A or 200A to match the alternator’s full output, not the average charge current.

Setup and Troubleshooting Tips

Alternator won’t start charging. The energize input isn’t wired, or isn’t powered when the engine runs.
Lithium house bank undercharging, or overheating the alternator. An Argofet doesn’t limit current or change voltage. Each battery gets roughly the alternator’s own voltage, so a lithium bank can pull everything the alternator makes. Use a DC-DC charger such as the Orion XS instead.
Smart alternator. Variable voltage that drops to about 12.5V can leave house batteries undercharged. A DC-DC charger handles this better.
Mixed chemistries. Lead-acid and lithium need different charge voltages, which an isolator can’t provide.
Undersized model. A 100A isolator on a 130A alternator will overheat. Size up.

Sizing Worked Examples

The Argofet rating has to cover the full alternator output, because all of the alternator current passes through the isolator before it splits between batteries. Pick the model by two numbers: alternator amps and how many batteries you charge.

Vehicle or boat	Alternator	Batteries	Model that fits
Van: starter plus one house bank	90A	2	Argofet 100-2
Boat: starter plus two house banks	90A	3	Argofet 100-3
Truck: starter plus one house bank	160A	2	Argofet 200-2
Boat: starter, house and thruster battery	180A	3	Argofet 200-3

The total charge current never exceeds what the alternator makes. A discharged house bank simply takes a larger share of it than a nearly full starter battery, because each output only delivers what its battery will accept.

Installation Checklist

Alternator cable. Size it for the alternator’s maximum output and the length of the run, then add the right fuse near the source.
Output cables. Each battery output gets its own cable and fuse at the battery end.
Mounting. Choose a dry spot with air around the housing so it can shed heat under full alternator current.
Alternator voltage. If the alternator senses voltage at its own terminal, confirm the regulated voltage with a meter at each battery after install.
Lithium house banks. Read the DC-DC section above first; an isolator passes whatever current a lithium bank will draw.

Worked examples are arithmetic estimates from the published ratings above, not test results. Real numbers depend on temperature, cable runs, battery state and load.

Victron lists every Argo FET battery isolators variant, with datasheets, on its official product page.

FAQ

Argofet vs Cyrix combiner?

A Cyrix connects batteries together with a relay when voltage rises. An Argofet keeps them separate at all times and splits the charge current.

Can an Argofet work with a single-output battery charger?

Yes. Victron says it works with an alternator or a single-output battery charger.

Which size do I need?

At least your alternator’s maximum output: 100A or 200A.

Can it be used at 48V?

The datasheet covers 12V and 24V systems.

How many batteries can one Argofet charge?

The -2 models have two battery outputs and the -3 models have three. Choose the 3-output version if you have a second house bank or a separate thruster or windlass battery.

Sources: Victron Argofet Battery Isolators datasheet and product page (victronenergy.com); Victron Cyrix battery combiner page.