From AGM to Lithium: A Full Electrical Overhaul on a Dufour 50
How we transformed a bluewater cruiser's DC system into a 920 Ah, intelligently managed lithium platform — and why every part of the boat had to come along for the ride.
When the owner of this Dufour 50 came to us, the goal was straightforward on paper: more energy, longer range, faster charging, fewer compromises offshore. The path to get there was anything but. A modern lithium house bank doesn't just slot in where the old AGMs sat. To do it properly, every charge source on the boat — alternator, inverter/charger, generator start, bow thruster, engine start — has to be re-thought, re-cabled, and brought onto a single communications network that actually knows what's happening.
That's the project we'll walk through here.
The system at a glance
- Vessel: Dufour 50 sailing yacht
- House bank: 2 × Epoch 12V 460Ah V2 LiFePO₄ batteries in parallel — 920 Ah at 12V
- Inverter/charger: Victron MultiPlus 12V / 3000W / 120V
- Alternator: Stock alternator converted to external regulation
- Regulator: Arco Zeus with temperature-based charge control
- Alternator protection: Balmar Alternator Protect device
- Monitoring: Victron Cerbo GX with Touch 70 display
- Auxiliary charging: Victron DC-DC chargers for engine start, generator, and bow thruster banks
- Switching: EGIS dual remote at house bank, plus three Nav-station remote switches (House On/Off, House/Engine parallel, Engine start)
- Replaced: Lifeline AGM batteries, Magnum inverter/charger, two ACRs
The starting point
The vessel arrived with a legacy setup that had served its time well: Lifeline AGM house batteries, a Magnum inverter/charger, an internally regulated stock alternator, and a pair of ACRs handling auxiliary battery charging. Reliable, but limited — and not built to talk to itself. Charge sources operated independently. State-of-charge was a guess. And every time the alternator ran hard, it was charging without temperature feedback or a profile suited to lithium chemistry.
The owner wanted a boat ready for extended bluewater passages. That meant a system that could deliver real capacity, charge intelligently from multiple sources, and tell him exactly what was happening at any moment.
The new heart: a 920 Ah lithium house bank
We built the new house bank around two Epoch 12V 460Ah V2 LiFePO₄ batteries wired in parallel, giving the boat 920 Ah of usable lithium capacity at 12V.
Getting that bank installed properly took more than dropping batteries into the existing compartment:
- Custom battery cleats fabricated and fitted to secure the new batteries in place
- Battery straps and buckles fabricated for positive retention in a seaway
- 600A tinned copper positive and negative bus bars installed adjacent to the bank
- 2/0 AWG cables of equal length running from each battery to the buses (length-matched cabling matters — it's how you keep current sharing balanced between parallel batteries)
- Class-T and ANL fuse block fabricated for proper DC distribution protection
- Epoch inter-battery comms cable installed and DIP switches set for parallel operation
- Battery terminal boots over every connection
- An EGIS dual remote battery switch installed at the bank, with a 4/0 AWG cable feeding it from the positive bus
The bank now reports state-of-charge directly to a dedicated SoC gauge and a Bluetooth gateway — and, more importantly, into the wider Victron network we built around it.
Out with the Magnum, in with the Multiplus
The original Magnum inverter/charger was removed entirely — unit, cabling, remotes, the lot — and replaced with a Victron MultiPlus 12V / 3000W / 120V.
The MultiPlus dropped into the original Magnum location under the port saloon seat. From there:
- Existing AC In and AC Out circuits were terminated to the new unit, with breaker sizing verified
- Two length-matched 4/0 AWG positive cables run to Class-T fuses on the DC distribution block
- Two length-matched 4/0 AWG negative cables run to the 600A negative bus
- Firmware updated and the charge profile programmed to LiFePO₄ specs
- A Cat 6 communications cable run forward to the Nav station for Cerbo GX integration
That last point is the key one. The MultiPlus isn't a standalone device anymore — it's a node on the network.
The alternator: from stock to externally regulated
A stock internally regulated alternator and a lithium house bank are not friends. Lithium will accept everything an alternator can throw at it, indefinitely, until something gives — usually the alternator. So we converted the stock unit to external regulation and built around it.
- Alternator removed, converted to external regulation, and reinstalled with output cabling sized to minimise voltage drop
- Arco Zeus alternator regulator installed near the engine compartment with full terminations: power, ground, voltage sense, field, tach
- Balmar Alternator Protect device installed as a safety layer
- 500A shunt installed in the alternator output circuit and protected with a neoprene cover
- Battery and alternator temperature sensors fitted, so charge output is throttled by real-world conditions, not assumptions
- Firmware updated, charge profile programmed for LiFePO₄
- Cat 6 cable run to the Nav station, joining the network via VE.Can
The result: the alternator now charges hard when it can, backs off when it needs to, and the regulator and Cerbo are both watching it.
The brain: Victron Cerbo GX with Touch 70
Every charge source on the boat now reports into a Victron Cerbo GX, with a Touch 70 display mounted at the Nav station — installed neatly into the spot the old Magnum remote used to occupy.
- Cerbo powered from a dedicated 24/7 circuit with inline fuse protection
- House battery comms terminated to VE.Can port 1
- Arco Zeus regulator terminated to VE.Can port 2
- MultiPlus terminated to VE.Bus
- Firmware updated and full system programming completed
What that means in practice: the owner can stand at the Nav station and see, in real time, exactly what every battery and every charge source is doing — and pull up the same view remotely from anywhere with a connection.
Engine start, generator, and bow thruster: isolated DC-DC charging
The old setup used ACRs (automatic charging relays) to share charge between batteries. Functional, but blunt. We pulled the ACRs and replaced them with Victron DC-DC chargers — one each for the engine start battery, the generator start battery, and the bow thruster battery.
For each circuit:
- ACR removed from the port saloon seat
- Victron DC-DC charger installed in its place
- Fuse protection installed on both input and output sides
- Firmware updated and charge profile programmed to that battery's chemistry
DC-DC chargers give you isolated, profile-matched charging instead of a dumb voltage tie-in. Every auxiliary battery now gets the right charge curve for its chemistry, drawn cleanly from the lithium house bank.
The engine start circuit also got a switching upgrade: the engine battery switch was relocated from the companionway, with a new EGIS remote switch installed at the Nav station via 16/4 wire. A 2/0 AWG cable runs from the engine start switch to the second position on the dual EGIS switch at the house bank.
Switching, finally, where you actually need it
One of the smaller but most-loved changes: every battery switch is now at the Nav station, not the companionway (visible as the three illuminated buttons below the Touch 70 in the photo above).
- House On/Off remote switch
- House/Engine parallel switch
- Engine start battery remote switch
When something needs to happen fast at sea, the helm and Nav station are where the crew is. The companionway is where the weather is.
What the owner walked away with
On handover, we delivered:
- A full DC primary wiring schematic
- A Victron communications network schematic
- Every circuit, fuse, and switch labelled throughout the vessel
- A complete documented system test
- A walkthrough of the system end to end
The bottom line
The Dufour 50 left the dock with a 920 Ah lithium house bank, intelligent multi-source charge management across the alternator, inverter/charger, and three isolated DC-DC chargers, and a unified Victron communications backbone giving the owner full visibility through the Touch 70 and remotely.
LiFePO₄ chemistry alone gives you more usable capacity and faster charge acceptance. Externally regulated alternation with temperature-based control protects the hardware while it does it. And the Cerbo GX network ties it together so the owner isn't guessing — about state of charge, about what's charging, about what's failing.
It's a system built for the trips this Dufour 50 was made for: long passages, far from shore power, where the margin between "comfortable" and "compromised" is measured in amp-hours and confidence in your gear.
Considering a lithium upgrade for your own Dufour 50 or other cruising yacht? Get in touch — we'd be happy to talk through what a full electrical overhaul looks like for your boat.