A New Zealand catamaran question with a ten-year answer
A recent enquiry came from a team building a fully electric yacht in New Zealand. They were considering electric propulsion, solar generation and a substantial house battery bank. Their questions were practical: Have these marine batteries been used on real vessels? How does modular expansion work? And should the propulsion bank and onboard house bank use the same battery design?
The short answer is that a marine battery is never just a box of cells. It is part of a vessel-wide electrical energy system that must match the propulsion load, essential services, charging sources, operating environment, monitoring architecture and safety requirements.
The longer answer begins well before the KiwiVolt name was established.
2013: From yacht building to electric sailing
In 2013, our China-based company acquired a portfolio of assets associated with Germany's Pica Yachts. The name Pica came from a family moment: yacht designer Holger Henn's daughter pointed at a sailing boat as a child and called it “Pica”. The name stayed.
One of the projects that followed was the conversion of the Pica 964 platform into the electrically propelled Yu33. It was an early fully electric sailing yacht project using a Torqeedo electric outboard. More importantly, it showed our team that electric propulsion could not be treated as a simple engine replacement. Hull efficiency, weight distribution, charging, range, onboard loads and system controls all had to work together.
Public history from ALVA Yachts confirms that Pica Yachts began in 2013, produced smaller sailing and electric powerboats, and was led by experienced yacht designer Holger Henn. Pica's later development contributed to the foundations of ALVA Yachts and its larger solar-electric catamarans. Read the ALVA Yachts history.
Our work during this period also included relationships with established marine equipment suppliers, including Seldén Mast and Fischer Panda. These projects expanded our understanding beyond propulsion alone to rigging, onboard generation, charging and complete vessel integration.
2015: Learning from complete Torqeedo propulsion systems
By 2015, we had become a major Torqeedo sales and distribution partner in China. Working with complete electric propulsion systems gave the team direct exposure to a wide range of real-world applications, from lightweight dinghies and fishing boats to sailing yachts and catamarans.
The most useful lessons did not come from a brochure. They came from matching motor power to hull type, estimating practical range, selecting charging arrangements, supporting installation and seeing how customers actually used electric boats.
Torqeedo's own development history also reflects the wider industry's move from small electric outboards into complete high-voltage propulsion systems. Its Deep Blue platform was introduced as a fully integrated electric propulsion system, illustrating how batteries, motors, controls and charging increasingly became one coordinated system. Torqeedo company history.
2016: Building our first marine power system
In 2016, we began designing our first in-house marine propulsion energy system. The first installation was not visually sophisticated: it was a yellow enclosure mounted on a simple experimental-cat.
That early prototype mattered because it moved the team from integrating other manufacturers' equipment to taking responsibility for battery enclosure design, electrical protection, connections, weight, serviceability and operation on the water.
The early systems were modest by today's standards. One surviving development unit is marked 12.8V and 0.64kWh, with separate charging and discharge connections. Its hand-labelled enclosure records a stage when the team was still testing how a marine battery should be packaged, connected and maintained.
Ten years of iteration: What actually changed?
Marine battery development is not a straight line from a smaller box to a larger box. Each application exposes a different constraint.
Across successive development stages, our work expanded from low-voltage prototypes into standardised LiFePO4 packs, portable higher-voltage modules, sealed metal enclosures and multi-module systems. The design priorities increasingly included:
- protection against water ingress and corrosion;
- mechanical strength for vibration and vessel movement;
- safer high-current connections and service isolation;
- battery management with voltage, current and temperature protection;
- CAN and RS485 communication with vessel systems;
- easier installation, inspection and replacement;
- modular expansion for different vessel sizes;
- centralised shutdown and fault response;
- chemistry and enclosure choices based on power, weight and endurance requirements.
The current sixth-generation platform includes modular 51.2V 100Ah, 5.12kWh configurations for electric propulsion and specialist marine use. LiFePO4 and lighter NCM configurations serve different priorities; chemistry, discharge capability, weight and protection strategy must be selected for the vessel rather than treated as interchangeable marketing options.
From small boats to unmanned and research vessels
The systems developed over this period have been applied across a broad range of marine work, including small fishing craft, monohulls, multihulls, unmanned surface vessels and specialist research platforms.
Unmanned vessels create a particularly demanding design brief. A USV may operate for long periods without a person onboard to respond to warnings. Battery state, temperature, current, communications, fault isolation and emergency shutdown therefore become part of the mission system, not optional accessories.
Our project history also includes batteries for maritime and scientific organisations, cold-region work and deep-sea-related applications. Company project records include systems operating in environments around -30°C and extreme high pressure. These are application-specific outcomes, not a universal performance claim: low-temperature charging, discharge power, heating, insulation and cell chemistry must all be engineered for the mission.
Propulsion battery or house bank? They are different jobs
One of the most important lessons from electric vessels is that the propulsion battery and the house battery bank should be assessed separately.
A propulsion battery may need sustained high discharge power, rapid fault response, motor-controller communication, cooling and enough reserve to manoeuvre safely. A house bank supports lighting, navigation, refrigeration, pumps, communications, galley appliances and an inverter. Its design is usually driven by daily energy consumption, usable capacity and charging availability.
For example, a nominal 48V 600Ah house bank stores approximately 28.8kWh at exactly 48V, or about 30.7kWh when built around a 51.2V LiFePO4 architecture. The usable energy will be lower after considering the permitted depth of discharge, reserve margin, temperature and conversion losses.
For many vessels, LiFePO4 is a strong starting point for the house bank because of its cycle life, thermal characteristics and suitability for energy-focused operation. A weight-sensitive, high-power propulsion bank may justify a different chemistry, but only after the safety case and vessel-level trade-offs have been assessed.
How modular expansion works
Modularity can make a marine battery system easier to size, install, service and expand. Multiple compatible modules may be connected in parallel to increase energy capacity while maintaining the system voltage.
However, “stackable” must not be interpreted as permission to connect any two batteries together. Before expansion, the designer must confirm:
- nominal and operating voltage range;
- cell chemistry and series configuration;
- BMS firmware and communication compatibility;
- current-sharing behaviour;
- cable, fuse, contactor and busbar ratings;
- module age, state of health and allowable imbalance;
- central monitoring and emergency shutdown behaviour.
Older and newer modules, or modules of different capacities, should only operate together where the system architecture has been specifically validated for that combination.
Designing marine lithium systems in New Zealand
New Zealand's marine environment makes practical engineering especially important. Salt, moisture, vibration, limited installation space and remote operation can expose weaknesses that remain hidden in a workshop test.
Maritime New Zealand advises that lithium-ion installations must address risks such as higher current capability, temperature rise, physical damage and the potential loss of essential onboard services. Its guidance highlights battery management, ventilation, fire containment, alarms, alternative power for essential systems and appropriate design review.
Every vessel is different. Commercial projects should involve the appropriate naval architect, electrical engineer, recognised design approver and surveyor early in the process.
2025-2026: Bringing the experience to New Zealand
In 2025, the founder's family began preparing to relocate to New Zealand and establish a local base for the next stage of the business. Following the relevant immigration approvals in 2026, work progressed on a local showroom, warehouse and future production and research capability.
The long-term objective is to localise more of the work behind small propulsion batteries, specialist batteries, vehicle power systems, and residential and commercial energy storage. For New Zealand customers, local capability should mean more than keeping stock. It should support system assessment, configuration, after-sales service, product improvement and collaboration with boat builders, engineers and research organisations.
This is the next chapter of the same story that began with yacht design and a simple white battery box: learning from real vessels, improving the system and building around the application.
Frequently asked questions
What is the difference between a marine propulsion battery and a house battery?
A propulsion battery is designed around motor power, sustained discharge, control communication and safe manoeuvring reserve. A house battery is designed around daily energy consumption for onboard appliances and essential services. They may use the same system voltage, but they do not automatically require the same chemistry or protection architecture.
Is LiFePO4 suitable for a boat/yacht house bank?
Often, yes. LiFePO4 is commonly considered for house banks because it offers good cycle life and energy-storage characteristics. The final design still depends on daily loads, inverter power, charging sources, installation space, temperature and vessel approval requirements.
Can marine battery capacity be expanded later?
Yes, when the modules and system architecture are designed for expansion. Compatibility, current sharing, protection, communications and the condition of the existing modules must be checked before adding capacity.
Can old and new marine battery modules operate together?
Sometimes, but it is not automatic. Different ages, capacities, chemistries, BMS versions or operating limits can cause unequal current sharing and protection problems. The exact combination must be approved as part of the system design.
What does a BMS do on an electric boat?
A battery management system monitors cell voltage, current and temperature, controls safe operating limits and can trigger warnings or disconnection. In a marine propulsion system, it may also communicate with the motor controller, charger, vessel display and emergency shutdown system.
Can Kiwivolt integrate batteries with Torqeedo or other electric propulsion systems?
Integration depends on motor voltage, current demand, communication protocol, charging equipment and the propulsion manufacturer's requirements. Kiwivolt can assess the system architecture, but compatibility must be confirmed for the exact motor, controller and battery configuration.
What information is needed to size an electric boat battery?
Useful inputs include hull type, motor power, cruise speed and power, operating hours, required range, house loads, solar and shore charging, reserve requirements, available space, weight limits, cooling, monitoring and the vessel's survey or classification requirements.