Beneteau Oceanis 45 Lithium Battery Refit: A 1,380 Ah House Bank, Victron Quattro 5000W, and a Full DC System Overhaul
When a Beneteau Oceanis 45 is prepared for extended bluewater work, the electrical system is almost always the limiting factor. This refit replaced the boat's aging AGM house bank, original inverter, stock alternator, and entire auxiliary charging architecture with a fully integrated 1,380 Ah lithium platform built around Victron Energy components. Below is a complete walkthrough of the system, the engineering choices behind it, and what changed on this Oceanis 45 from before to after.
The system at a glance
- Vessel: Beneteau Oceanis 45
- House bank: 3 × Epoch 12V 460Ah V2 LiFePO₄ batteries in parallel — 1,380 Ah at 12V
- Inverter/charger: Victron Quattro 12V / 5000W / 120V
- AC balancing: Victron Auto Transformer for 120/240V split-phase
- Alternator: Arco 275A 12V high-output, externally regulated
- Regulator: Arco Zeus with temperature-based charge control
- Monitoring: Victron Cerbo GX with Touch 70 display and Smart Shunt
- Auxiliary charging: Victron DC-DC chargers for engine start and bow thruster banks
- Shore power limit: 30 A AC input
- Repurposed Cristec chargers: reassigned to engine and thruster banks
Why a lithium refit changes everything
Legacy AGM banks limit an offshore yacht in three ways: usable capacity is roughly half the rated capacity, recharge slows dramatically above 80% state of charge, and there's no real-time visibility into what each charge source is doing at any given moment. LiFePO₄ chemistry inverts every one of those constraints. You get nearly the full nameplate capacity, fast charge acceptance throughout the cycle, and — when paired with a proper communications backbone like the Victron Cerbo GX — a system that actually knows what it's doing and tells you about it. For a vessel headed offshore, that is the difference between rationing electricity and using it.
The 1,380 Ah lithium house bank
Three Epoch 12V 460Ah V2 lithium batteries were installed in parallel under the port aft bunk. Each was secured with custom-fabricated starboard battery cleats and straps, with length-matched 2/0 AWG cables running from each negative terminal to a 600 A copper bus bar. A bespoke fuse block of three Class-T fuses was fabricated and mounted next to the bank, with length-matched 2/0 AWG positive cables to each battery and a 4/0 AWG cable feeding the new house On/Off switch.
A Victron Smart Shunt sits at the negative bus, sending live state-of-charge data via VE.Direct to the Cerbo GX. House and engine battery voltage sensing are wired through the shunt with inline fuse protection. Firmware was updated and the shunt programmed to the Epoch battery profile during commissioning.
Inverter/charger: Victron Quattro 5000W with Auto Transformer
The original inverter was removed entirely and replaced with a Victron Quattro 12V / 5000W / 120V, mounted in the space freed up under the starboard aft bunk. To handle the vessel's 120/240V split-phase AC system on a 30 A shore connection, a Victron Auto Transformer was installed near the main breakers. One leg from the autotransformer feeds the Quattro; the other feeds non-inverter loads. This configuration automatically balances 120V branch loads across the 240V supply, preventing leg imbalance from tripping the main breaker.
Two parallel runs of 4/0 AWG cable connect the Quattro's negative posts to the ship's negative bus. Another two runs feed the positive side through Class-T fuses on the load fuse block. AC output circuits from the original inverter were re-routed to the Quattro. A 16/2 control cable handles the Quattro's ground-relay coordination with the Auto Transformer, and a Cat 6 line runs to the Cerbo GX. AC input is current-limited to 30 A to protect the shore connection during heavy charging.
Alternator: 275 A external regulation, properly cooled
The factory alternator was removed and replaced with an Arco 275A 12V high-output alternator, externally regulated by an Arco Zeus controller. Output runs through a 4/0 AWG cable to a Class-T fuse on the DC distribution; the isolated ground returns to the negative bus on its own dedicated 4/0 conductor. The original battery isolator — redundant under external regulation — was identified and removed along with its associated cabling.
The Zeus regulator was wired with the full sensor suite: alternator temperature sensor, battery voltage sense with fuse protection, field, ignition, stator, and a current shunt covered in neoprene. A Balmar Alternator Protect device was added as a safety layer against overvoltage events. Critically, a 3-inch blower was installed on the existing engine-room duct with a dedicated branch directing cool air across the alternator. A 275 A unit puts out real heat under sustained load, and adequate cooling is what keeps it healthy long-term.
Cerbo GX: the system's nervous system
The Victron Cerbo GX was mounted behind the AC/DC panel, powered from a 24/7 fused circuit. It receives VE.Direct from the Smart Shunt, Cat 6 from the Arco Zeus regulator, and Cat 6 from the Quattro. The Touch 70 display was installed at the main panel, giving the crew live visibility of every battery, every charge source, and the AC inputs and outputs. Where Starlink is fitted, the Cerbo can be tied in for remote monitoring and alerting from anywhere with a connection.
Engine and thruster: isolated DC-DC charging
Auxiliary banks are now charged through dedicated Victron DC-DC chargers rather than the older voltage-tie or isolator approach. The engine start battery is fed by a DC-DC charger sitting between the 1/2/Both switch and the load bus, with fuse protection on input and output. The bow thruster bank is charged identically from its own DC-DC charger off the load fuse block. Each charger was firmware-updated and programmed to the correct profile for its battery chemistry. The vessel's existing Cristec chargers were repurposed — their original house-bank circuits were removed, and they were reprogrammed to top off the engine start and thruster banks.
Documentation, finishing, and handover
Every primary DC cable was sleeved in split loom and secured with saddles and zip ties. Every switch and fuse onboard was labelled. The vessel's 120V single outlets were swapped for double outlets, with new outlet boxes fabricated where the openings needed enlarging. On handover, the owner received a full DC primary schematic, a documented system test, and a walkthrough covering every node on the network.
The outcome
The vessel left the dock with 1,380 Ah of usable lithium capacity, a 5,000-watt inverter capable of running heavy 120/240V loads directly from battery, a 275 A alternator that recharges intelligently under temperature-based control, and a unified Victron Cerbo GX backbone that ties every component into one coherent, monitorable system. It's a setup built for what Oceanis 45 owners buy these boats to do: cruise far, stay out longer, and never have to wonder what the electrical system is doing at three in the morning.