Wiring, charging, safety, compliance
Marine Lithium Battery Installation Guide
Everything that sits between a lithium bank and a boat that keeps working: charging from engines, solar and shore; cable, fusing and monitoring; ventilation and fire; and what AS/NZS 3004.2, your insurer and the marina will each want to see.
DC-DC sizing · Live for a 400 Ah bank
Alternator limits and DC-DC charger sizing
We take a quarter of the bank’s capacity as the ceiling the cells should be asked to accept on an alternator, and half of the alternator’s rating as the ceiling the alternator should be asked to sustain. The smaller of the two, rounded down to a charger you can buy, is the answer. The highlighted row is your alternator from the calculator.
| Alternator | DC-DC to fit | Why |
|---|---|---|
| 40 A | 18 A | Mandatory — alternator cannot sustain the bank |
| 60 A | 30 A | Mandatory — alternator cannot sustain the bank |
| 90 A | 40 A | Recommended — protects regulation and warranty |
| 120 A | 60 A | Recommended — protects regulation and warranty |
| 150 A | 60 A | Recommended — protects regulation and warranty |
In this cluster
Marine battery wiring, charging and protection guides
Refit planningMarine Battery Refit Quotes: Scope and Comparison ChecklistCompare the complete installed system: battery, protection, charging, monitoring, labour and handover. Two quotes for the same amp-hours can describe very different jobs.Before you buyBoat Battery Compartment Measurements and Layout ChecklistMeasure the access opening, installed clearance, terminal space and restraint points—not just the battery tray. A battery that fits on paper may be impossible to service aboard.Energy planningBoat Battery Energy Log: Measure Weekend Power UseRecord energy used across a representative day and night, together with charging and weather. A useful energy log separates appliance demand from the energy returned by solar or the engine.Everyday loadsBoat Fridge Power Consumption: Measure Daily Energy UseUse measured daily energy, not compressor current multiplied by 24. Fridge demand changes with temperature, ventilation, insulation and how often the lid or door opens.Cruising rangeBoat Battery Reserve Capacity for Cloudy Days at AnchorSize a low-solar scenario explicitly. Choose which loads must keep running, how long you need them and the charging option available before the reserve is exhausted.Solar planningBoat Solar Panel Shading: Output and Layout ChecklistPhotograph the array through the day and compare controller energy readings under similar conditions. Rigging, aerials and the boom can make nominal panel capacity a poor guide to daily yield.Everyday loadsBoat Inverter Standby Power: Measure Idle Battery DrainAn enabled inverter can consume power with no appliance running. Check the model’s idle and search-mode specifications, then measure the behaviour of your actual installation.MonitoringBoat Battery Monitor State of Charge Drift: Causes & ChecksA monitor estimates state of charge from measured current and configured assumptions. Wrong capacity, bypassed current paths or missed synchronisation can make the percentage drift.System recordsBoat Battery Charger Settings Record: What to DocumentRecord every charging source, its profile, current limit and temperature behaviour. Keep the approved settings and equipment manuals together so a reset or replacement does not erase the system design.CommissioningMarine Lithium Battery Commissioning & Handover ChecklistAsk for a labelled system diagram, equipment and protection details, approved settings, applicable documentation and a demonstration of normal operation, alarms and isolation.Seasonal careBoat Lithium Battery Winter Storage Planning ChecklistFollow the battery maker’s storage instructions, account for every remaining load and confirm what charging can do in cold conditions. Storage is a system plan, not just a battery percentage.MaintenanceBoat Battery Terminal Corrosion: Saltwater Inspection GuideLook for moisture, corrosion, damaged insulation, loose restraints and signs of heat without disturbing live connections. Have suspect high-current wiring assessed before continuing normal use.Cruising preparationRemote Cruising Battery Spares and Support ChecklistCarry the exact approved consumables, offline documentation and a clear fault-response plan. Spares are useful only when you know the correct part and can replace it safely.Buying a boatUsed Boat Lithium Battery Inspection: Records to CheckAsk for the installation history, equipment identities, diagram, settings and supporting records. A tidy battery case and a full-charge display do not establish the condition of the system.Fishing boatsTrolling Motor Lithium Battery Bank Planning GuideCheck motor voltage, current, duty cycle and the battery’s permitted configuration first. A dedicated motor bank can simplify planning, but its charging and protection still need a complete design.ChargingMarine DC-DC Chargers: Purpose and Alternator ProtectionEngine charging needs a compatible, current-managed design. A DC-DC charger is one common approach; a properly designed alternator regulator and BMS arrangement can be another.CompatibilityLithium Battery Alternator Overheating: Causes on BoatsIt can if the charging system is not designed for the lithium bank. Sustained demand can overheat an alternator, and an abrupt battery disconnection can create a separate protection problem. Check current management, temperature control and BMS behaviour together.WiringMarine Lithium Battery Wiring: Cable and Fuse ProtectionA Class-T or equivalent fuse at the bank terminal, cable sized for the charger and inverter currents rather than the old lead-acid runs, and terminations you would trust in a seaway.WiringBoat Battery Shunt Placement: Wiring and Bypass ErrorsOn the negative, between the bank and everything else on the boat. Without it you are guessing at state of charge, and lithium's flat voltage curve makes guessing useless.Shore powerLithium Boat Battery Mains Charger Compatibility ChecksOnly if it has a genuine lithium profile. Lead-acid float voltages and desulphation pulses are exactly what a BMS disconnects from.SafetyLithium Boat Battery Ventilation and Fire Safety PlanningLiFePO4 does not vent hydrogen the way lead-acid does, but it still needs a sealed, restrained and ventilated compartment, and your insurer will want to see one.ComplianceAS/NZS 3004.2 and Marine Lithium Battery InstallationsIt sets requirements for electrical installations on boats. How it applies, and whether licensed or certified work is required, depends on vessel category, jurisdiction, voltage and the work performed.ComplianceBoat Insurance and Lithium Batteries: Questions to AskWhat the BMS is, whether the enclosure is restrained and ventilated, how the bank charges from shore and engine, and who certified the work. Have the answers written down before you are asked.WarrantyOutboard Warranty and Lithium Boat Battery CompatibilityNot by itself. What voids it is the charging arrangement — a lithium house bank on the engine's charging circuit without current limiting.SafetyLiFePO4 Cold Charging on Boats: Temperature LimitsNot below 0 °C without low-temperature protection or heating. Discharging is fine; it is charging that damages cold cells, permanently and invisibly.InstallAGM and Lithium Batteries on a Boat: Separate Bank DesignYes, on separate banks with separate charge profiles. No, on the same bus. The lithium takes every amp and the AGM sits chronically undercharged.InstallMarine Battery BMS Explained: Protection and ShutdownThe Battery Management System protects the cells by disconnecting them from the boat. That protection is a feature until it happens at three in the morning with the fridge full.
The insurer’s checklist
Lithium battery installation documents and insurer questions
Nine items that appear, in one form or another, on every Australian underwriter’s lithium questionnaire we have seen. Tick what your install already has. The rest is the conversation to have with your electrician.
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