Collection: Storage

Boat electrical storage: batteries, protection, and energy management

Boat electrical storage isn't just about choosing a capacity in amp-hours. A reliable installation combines a battery suited to the sailing program, a BMS or cut-off protection when the chemistry requires it, a way to measure the actual state of the battery bank, and switching devices sized for the vessel's currents.

This collection groups the components that structure the battery bank: lithium and lead batteries, BMS, battery disconnect switches, battery monitors, charge relays, contactors, and disconnectors. The goal is to build a readable, maintainable architecture capable of powering instruments, the autopilot, VHF, windlass, lighting, refrigeration, and comfort systems without risking the starter battery.

Major storage categories

• Batteries: LiFePO4/LFP batteries, service batteries, and batteries suited for 12 V, 24 V, or 48 V banks. Victron Smart, SuperPack, Lithium NG, Mastervolt, and MG Energy ranges should not be chosen solely based on capacity: check charge current, discharge current, required BMS, and charging temperature.
• BMS batteries: smallBMS, BMS NG, Smart BMS, and Lynx Smart BMS modules to monitor lithium cells, authorize or cut charge and discharge, and prevent overcharging, deep discharge, or charging at low temperature.
• Battery disconnect switches: manual or remote-controlled switches to isolate a bank, cut a main circuit, or temporarily combine two batteries. The m-Series, e-Series, and ML-RBS families do not cover the same currents or uses.
• Battery monitors: shunts and displays like SmartShunt, BMV, or M2 DC to measure voltage, current, state of charge, and history. A monitor informs; it does not replace electrical protection.
• Charge relays: ACR, SI-ACR, BatteryLink, and ML-ACR to automatically charge two battery banks from a common source, then isolate them when voltage drops.
• Contactors, solenoids & disconnectors: L-Series solenoids, ML contactors, m-LVD, and ATD to control or cut a power circuit, protect against low-voltage discharge, or delay a cut-off.

Lithium, lead, AGM: the choice depends on the architecture

Lithium LiFePO4 offers weight savings, greater usable depth of discharge, and more stable voltage. In return, it requires a more rigorous architecture: compatible BMS, charge and discharge cut-off, alternator protection, properly sized fuses, and sometimes a DC/DC charger or external regulator depending on the engine and installed bank.

Lead, AGM, or gel batteries remain relevant for simple uses, engine starter batteries, or installations where robustness and tolerance outweigh energy density. They handle repeated deep discharges less well, but their integration can be more straightforward in an existing architecture.

What to size before ordering

• Daily consumption: instruments, autopilot, lighting, refrigeration, communication, pump, computer, inverter. Without an energy balance, battery capacity is a fragile estimate.
• Maximum currents: windlass, thruster, inverter, starter, charger, and alternator dictate cable cross-sections, fuses, battery disconnect switches, and contactors.
• Charging sources: engine alternator, shore power charger, MPPT solar, hydrogenerator, generator, or inverter-charger have different profiles and limits.
• Bank separation: the starter battery must remain available. Charge relays and ACRs serve a different purpose than contactors or low-voltage disconnectors.
• Monitoring: a bank that isn't measured often leads to misinterpretation. A correctly configured shunt is more reliable than a voltage reading alone.

Common mistakes

• Comparing two batteries solely on Ah without considering voltage, chemistry, permissible current, and BMS compatibility.
• Replacing lead with lithium without revising the alternator charging, cut-off thresholds, and main fuse.
• Installing an undersized battery disconnect switch or contactor relative to the actual current of the windlass or inverter.
• Confusing monitor, BMS, and circuit breaker: measuring, protecting, and cutting are three different functions.
• Neglecting maintenance: accessibility of fuses, cable labeling, terminal tightening, and onboard schematic documentation.

Skysat advice

For a reliable storage installation, start with the complete schematic rather than an isolated battery spec sheet. Define consumers, charging sources, battery chemistry, protections, and cut-off modes. A high-end lithium battery poorly integrated can be less reliable than a simpler bank that is properly protected.

On a refit, we first check the existing wiring, grounds, DC distribution, available space, ventilation, and alternator capacity. Only then do we select the battery, BMS, monitor, and switching devices. It is this overall coherence that makes the difference at sea.