Collection: Batteries

Marine batteries: choosing the right capacity for your onboard system

The battery is the boat’s energy reserve: it powers electronics, refrigeration, lighting, pumps, windlass, bow thruster, autopilot, and sometimes a 230 V inverter. The right choice isn’t just about ampere-hour capacity. It depends on usage, chemistry, bank voltage, charge current, discharge current, available weight, and the protections installed around the bank.

This collection includes marine service batteries, starter batteries, and dual-purpose batteries for 12 V, 24 V, 36 V, and 48 V architectures. It complements the BMS batteries, battery monitors, battery relays, fuses, and battery disconnect switches collections, essential for building a reliable system.

Major battery families

• AGM: robust, maintenance-free, and well-suited for starting, simple service banks, and installations that must remain close to a classic lead-acid system.
• Gel: suitable for service loads and regular discharges, with good cycling performance when charging is properly regulated.
• LiFePO4 / lithium: lighter, faster to charge, and capable of delivering a higher usable energy share, provided a BMS, appropriate charging, and robust protections are in place.
• Dual-purpose service + starter batteries: useful when the installation requires a compact format or versatile use, but must be sized carefully based on current demands.

Available ranges

• Victron Lithium NG 12.8 V 200 Ah, 12.8 V 100 Ah NG, 12.8 V 150 Ah NG, and 25.6 V 300 Ah NG: next-generation LiFePO4 batteries designed to integrate with the Victron BMS.
• Victron Lithium SuperPack 12.8 V 200 Ah NG and SuperPack 12.8/25.6 V formats: compact lithium solutions for installations where integration must remain simple.
• Mastervolt MLI Ultra 12/3000, MLI Ultra 24/6000, and MLI Ultra 12/6000: lithium batteries for Mastervolt-integrated systems and high-capacity banks.
• Mastervolt MVG Gel 12 V 200 Ah, AGM 12 V 270 Ah, and AGM SlimLine 12 V 185 Ah: premium lead-acid batteries for replacement, service, or classic banks.
• Solid State Marine 12 V 90 Ah, 12 V 300 Ah dual-purpose service + starter, and 48 V 210 Ah: lithium/solid-state batteries for modern service architectures, including high voltages.
• Optima BlueTop 12 V 50 Ah: AGM marine battery designed for starting and compact applications.

Sizing a battery bank

To size correctly, start with the boat’s actual power consumption: fridge, autopilot, instruments, lighting, anchoring, communications, bilge pump, watermaker, inverter, or electric motor. Usable capacity is not the same as nominal capacity. A lead-acid battery is typically used with a more limited depth of discharge, whereas a LiFePO4 bank can deliver a higher share of its capacity with more stable voltage.

• Simple coastal use: a 12 V AGM or Gel bank may remain suitable if loads are low and charging sources are conventional.
• Cruising with anchoring: lithium becomes advantageous to save weight, handle higher charge currents, and increase usable autonomy.
• High-power consumers: inverters, windlasses, bow thrusters, watermakers, or electric cooking require verification of continuous discharge current, peak loads, and cable cross-sections.
• 24/48 V architecture: useful for reducing current and losses, but requires full consistency between batteries, chargers, alternator, inverter, and protections.

Lithium: don’t forget the ecosystem

A lithium battery is never chosen in isolation. It must be compatible with the BMS, charging sources, isolation relays, fuses, battery monitor, and charging parameters. In a Victron installation, a Lithium NG battery is designed to work with the NG BMS, monitoring network, and compatible chargers. In a Mastervolt installation, MLI Ultra batteries perform best within a coherent MasterBus or CZone system.

The battery monitor tracks state of charge and consumption. The BMS protects the cells. Fuses protect the wiring. The battery disconnect switch isolates the bank for maintenance or emergencies. These functions are not interchangeable.

Common mistakes

• Comparing ampere-hours alone without considering the actual usable depth of discharge.
• Replacing lead-acid with lithium without checking alternator, shore charger, solar, DC-DC, BMS, and safety cut-off.
• Installing a battery capable of high currents without adapting cables, terminals, fuses, and disconnect switches.
• Mixing batteries of different ages, technologies, or capacities in the same bank.
• Choosing a battery based solely on price, while accessibility, ventilation, weight, mounting, and after-sales service are equally important.

Skysat’s advice

For a marine battery, the right question isn’t just "how many Ah?", but "how much usable energy, at what current, with what protections, and what charging?". We recommend starting with a power consumption audit, then selecting the technology and bank voltage before choosing capacity. This approach ensures a bank that is clear, reliable, and maintainable onboard.