Cosa consuma la batteria di un drone subacqueo? Propulsori, correnti, luci, sonar e carichi utili

Thrusters normally drain an batteria per droni subacquei faster than any other variable load, especially when an ROV must accelerate, hold position or work against a current. Lights, sonar, cameras and other electronics may draw less power individually, but their continuous operation still matters over a long dive.

Payloads complicate the picture further. Some consume electricity directly; others increase drag or disturb buoyancy and trim, forcing the propulsion system to work harder. That is why useful runtime cannot be predicted from battery amp-hours alone. The entire mission profile has to be considered.

What Drains an Underwater Drone Battery the Fastest?

For most battery-powered ROVs, propulsion is the largest variable demand on the battery. The difference between cruising gently through still water and holding position in a strong current can therefore be more important than the capacity figure printed on the pack.

Thruster Load: Speed, Acceleration and Station-Keeping

Thruster power rises as the vehicle asks for more thrust. As a real engineering reference, Blue Robotics specifies its T200 thruster at 205 W at full throttle on 12 V, 390 W at 16 V and 645 W at 20 V. Those figures apply to a single thruster under the stated conditions, not to every ROV or every operating point.

An ROV rarely runs every thruster at maximum output continuously. Nevertheless, repeated acceleration, aggressive manoeuvring and station-keeping increase the duty cycle of the propulsion system. The battery must supply not only the average mission load but also the higher currents created during demanding manoeuvres.

This distinction explains why nameplate battery capacity cannot provide a reliable runtime figure on its own.

Currents, Tether Drag and Position Holding

Water current does not electrically connect to the battery, but it can increase battery drain substantially by increasing the thrust needed to maintain course or position.

A tether can add another load. Excess cable in the water increases hydrodynamic drag, while excessive tether tension makes the vehicle work against the cable. Boxfish Robotics identifies thruster speed, joystick demand, LED lighting, tether drag, tether tension, current and swell among the variables that affect ROV battery use.

This is particularly important in deeper operations. Current can act on tens or hundreds of metres of tether as well as on the vehicle itself. Operators discussing wreck inspection and deeper-water ROV work repeatedly raise current and tether drag as practical concerns, which helps explain why calm-water runtime rarely transfers directly to more demanding sites.

Why Rated Runtime and Mission Runtime Differ

Published runtime normally reflects defined or typical operating conditions, not continuous maximum-thrust operation.

Blue Robotics, for example, lists approximately two hours of normal use and four hours of light use for a BlueROV2 fitted with its 15.6 Ah battery. The same battery therefore produces very different operating times simply because the vehicle is being used differently.

For an underwater drone battery, a more useful question is not simply, “How many hours does it last?” It is, “How many watt-hours will this specific mission consume?”

How Much Power Do Lights, Sonar and Onboard Electronics Use?

Lights, sonar and onboard electronics usually draw less instantaneous power than hard-working thrusters, but many of these loads remain active for most or all of the dive.

Lighting in Low-Visibility Water

Lighting demand depends on water clarity, operating depth, camera requirements and lamp output. Clear, shallow water may require little additional illumination, while inspections inside structures or in turbid water can require powerful lights for most of the mission.

That creates a simple operational trade-off: reducing unnecessary light output can save energy, but visibility requirements still come first. Dimming is often more useful than treating lighting as a binary on/off load.

Boxfish specifically identifies depth and visibility, and the resulting use of lights, as factors affecting battery endurance.

Sonar, Cameras and Navigation Sensors

Sonar, cameras and navigation sensors create what engineers often treat as part of the vehicle’s continuous or “hotel” load. Individual devices may appear modest beside a propulsion system, but a load running for three hours consumes three times the energy it would use in one hour.

One published ROV power-system modelling example includes six thrusters alongside a 7 W sonar, camera, dimmable LED light and control electronics. More importantly, the example changes the duty cycle of those loads between roaming, scanning and inspection phases rather than assuming that everything operates at full power throughout the dive.

That is the right way to evaluate sonar or camera demand: use the actual device specifications and the percentage of the mission for which the equipment will operate.

Always-On Electronics and Conversion Losses

Computers, communications hardware, sensors and BMS electronics can run continuously even while an ROV is nearly stationary.

DC-DC converters also introduce losses whenever the battery voltage has to be converted to separate rails for thrusters, cameras, sonar or control electronics. A few watts of continuous auxiliary demand may seem unimportant beside a high-power thruster, but those watts accumulate throughout a long survey.

For mission planning, every persistent load belongs in the energy budget.

How Do Payloads Increase Underwater Drone Battery Drain?

Payloads can shorten runtime in two different ways: some draw electrical power directly, while others make the propulsion system work harder.

Powered Payloads vs Passive Payloads

A sonar, manipulator, additional camera or auxiliary light is a powered payload. Its electrical consumption can be added directly to the mission power budget.

A passive payload may have no electrical connection at all, yet still reduce endurance. A sensor frame, sample basket or protective structure can increase frontal area and drag. Additional mass can also require changes to buoyancy material and vehicle balance.

The distinction matters because removing a low-power electrical device may save less energy than correcting a badly integrated passive payload.

Buoyancy, Trim and Hydrodynamic Drag

An ROV that is close to neutral buoyancy and properly trimmed needs less continuous corrective thrust than one that persistently wants to rise, sink, pitch or roll.

Deep-water engineering makes the relationship more complicated. Stronger pressure housings tend to add mass, which in turn requires additional buoyancy. Woods Hole Oceanographic Institution notes that heavier pressure-resistant structures can make underwater robots more cumbersome and increase battery consumption.

For this reason, specifying a battery for underwater drone projects is partly a mechanical-design problem. Battery mass, enclosure size, buoyancy and placement all influence the energy needed to move the complete vehicle.

Manipulators, Tools and Extra Thruster Work

Manipulators and powered tools create direct electrical or hydraulic demand, but using them can also increase the time spent station-keeping.

An inspection ROV may reach the worksite efficiently and then spend much of the dive maintaining a precise position while operating a gripper, sonar or inspection instrument. In that situation, the combination of payload demand and propulsion demand matters more than either load in isolation.

The battery should therefore be sized around the mission phase with the greatest sustained combined demand, not simply the vehicle’s cruising requirement.

Which MANLY Battery Packs Suit Different ROV Power Systems?

MANLY Battery offers LiFePO4 robot-battery platforms that can provide starting points for compatible ROV and underwater-robot power architectures. They should be matched to system voltage, average and peak current, available space, BMS requirements and the project’s pressure-housing design. Their IP ratings should not be interpreted as subsea operating-depth ratings.

MANLY 24V 30Ah LiFePO4 Robot Battery for Compact ROV Power Systems

25.6 V nominal | 30 Ah | 768 Wh | 30 A continuous discharge | 60 A peak for 1–3 seconds

This compact LiFePO4 battery platform is suited to projects whose verified electrical architecture falls within its voltage and current limits. The 768 Wh energy content provides a useful starting point for smaller inspection robots and moderate-power systems, while optional RS485, RS232 and CANBus communication can support integration with a vehicle controller or monitoring architecture.

MANLY can also customise dimensions, housing, connector and BMS-related requirements. That flexibility matters when the battery must fit a pressure housing rather than dictate its shape. The robot-battery specification lists IP65 protection, so subsea use still requires a properly engineered pressure-rated enclosure or another project-specific underwater integration method.

MANLY 24V 60Ah LiFePO4 Robot Battery for Higher Energy Demand

25.6 V nominal | 60 Ah | 1,536 Wh | 60 A continuous discharge | 120 A peak for 1–3 seconds

Doubling the capacity to 60 Ah gives this 24 V platform 1,536 Wh of nominal stored energy while also raising the continuous and short-duration discharge capability. That combination is relevant to robots with more demanding thruster duty cycles, longer missions or a larger suite of powered sensors and tools.

The pack supports optional RS485, RS232 and CANBus communication, and the housing dimensions are customisable. For ROV integrators, those features make the platform useful when the battery, BMS and mechanical enclosure need to be designed as part of the same architecture rather than treated as separate components.

MANLY 48V 60Ah LiFePO4 Robot Battery for Higher-Voltage Architectures

51.2 V nominal | 60 Ah | 3,072 Wh | 60 A continuous discharge | 90 A peak below 1 second

The 48 V-class platform stores substantially more energy and is aimed at systems designed around a compatible higher-voltage electrical architecture. Higher system voltage can reduce current for a given power level, but every motor controller, converter, connector and protection device must be designed for that voltage.

MANLY lists both ABS and metal enclosure configurations, with IP67 and IP65 protection respectively, together with optional communication and OEM customisation. These ingress-protection ratings are useful enclosure specifications, but the pack still needs pressure-qualified integration before use at ROV operating depth.

For an OEM or integrator, the important role of a battery manufacturer is therefore not simply supplying more amp-hours. The produttore di batterie needs the vehicle voltage, power profile, peak-current duration, available dimensions, communication requirements, charging method and mechanical environment before a suitable pack can be specified.

How Do You Calculate Underwater Drone Battery Runtime Before a Dive?

A realistic runtime estimate starts with watt-hours and average mission power, then adds losses and operating reserve.

Build a Mission Power Budget in Watts

List every significant load and divide the mission into operating phases such as:

• transit;
• station-keeping;
• sonar scanning;
• visual inspection;
• manipulator or tool operation.

For each phase, estimate the power used by the active thrusters, lights, sonar, cameras, computers and auxiliary equipment. Then calculate the time-weighted average.

This is more reliable than adding the maximum rating of every component, because most ROVs do not operate every subsystem at maximum demand simultaneously.

Convert Watt-Hours into Estimated Runtime

Battery energy is:

Energia (Wh) = Tensione nominale (V) × Capacità (Ah)

A preliminary runtime calculation is then:

Estimated runtime (hours) = Planned usable battery energy (Wh) ÷ Average mission power (W)

Suppose a system has 1,500 Wh of nominal energy, the mission plan allows 80% of that energy for normal operation, and the weighted average load is 600 W:

1,500 × 0.80 ÷ 600 = 2.0 hours

That is an engineering estimate, not a promised field runtime. Real missions still need allowance for conversion losses, current, temperature, battery ageing and recovery reserve. Energy budgeting for underwater robots similarly needs to include propulsion, sensors, lighting, communications and other loads rather than Ah alone.

Add Margin for Currents, Power Spikes and Temperature

An ROV should not be planned to reach zero usable energy at the end of a normal mission.

Reserve needs to cover unexpected current, longer station-keeping, route changes, recovery delays and the gradual reduction in available battery performance with age. Cold battery temperatures can also increase internal resistance and reduce available power in lithium-ion cells, so room-temperature figures should not automatically be treated as cold-water performance.

The appropriate reserve is mission-specific. A battery for underwater drone inspection in a sheltered tank has different recovery requirements from one used offshore in variable current.

Which Battery Specifications Matter Beyond Capacity?

Capacity tells you how much nominal energy is stored. It does not tell you whether the pack can safely supply the required current, fit the vehicle or communicate with its control system.

Corrente di scarica continua e di picco

Three figures should be separated:

• corrente di missione media;
• maximum sustained current;
• short-duration peak current.

Thruster startup, rapid acceleration, station-keeping and simultaneous tool use can create short peaks well above the average load.

High internal resistance also produces voltage drop under load. If voltage falls far enough, propulsion performance can decline or protection electronics may activate even though significant nominal capacity remains. Underwater battery design therefore needs to consider the complete high-current path through cells, BMS, busbars, cables, connectors and motor controllers.

Voltage, BMS and Communication

The battery voltage must match the electrical architecture, not merely the nominal voltage printed on a thruster.

A BMS should be selected around the required charge and discharge limits, over-current protection, temperature monitoring, balancing and fault handling. For commercial robots, communications such as CANBus or RS485 can also make state-of-charge and fault information available to the vehicle controller.

This is where a configurable Batteria LiFePO4 can be valuable: electrical limits, BMS behaviour, connector arrangement and physical packaging can be developed around the platform rather than forcing the platform around a generic pack.

Why IP67 Is Not a Depth Rating

An IP67 rating does not mean a battery is qualified for operation at normal ROV diving depths.

IEC 60529 defines enclosure ingress-protection classifications. Standard IPX7 testing represents temporary immersion under specified conditions; commonly applied IEC 60529 test conditions use approximately 1 metre of water for 30 minutes.

Deep-water equipment faces an entirely different pressure environment. At an average seafloor depth of 3,800 metres, WHOI notes that hydrostatic pressure is roughly 380 times atmospheric pressure. Pressure housings for batteries and electronics therefore need to be engineered and validated for the intended depth.

Water resistance and pressure qualification must remain separate specifications. The same distinction is important when integrating any MANLY LiFePO4 battery into a subsea vehicle.

How Can You Reduce Underwater Drone Battery Drain During a Mission?

The largest efficiency gains often come from reducing unnecessary propulsion work before switching off useful sensors.

Reduce Thruster Work Before Cutting Sensor Use

Avoid sustained high thrust when a lower speed can complete the same task. Plan approaches so the ROV does not repeatedly accelerate, reverse or fight the current unnecessarily.

For inspection work, positioning the vehicle so that the current assists rather than opposes the planned route can reduce station-keeping demand. The exact strategy depends on the site, tether and vehicle configuration, but the objective is consistent: spend fewer watt-hours generating avoidable thrust.

Manage Lights, Sonar and Payload Duty Cycles

Use lighting output appropriate to the camera and visibility rather than automatically running every lamp at maximum brightness. Sonar and other instruments can also be scheduled around the phases in which their data is actually required, provided that doing so does not compromise the mission.

The same principle applies to manipulators and other powered payloads. Mission planning should identify when each load is required instead of assuming every accessory operates continuously.

Keep Thrusters, Trim and Tether Efficient

Good mechanical setup saves electrical energy.

Maintain neutral or intentionally controlled buoyancy, correct poor trim before deployment, minimise unnecessary tether in the water and check thrusters for fouling or damage. A poorly balanced vehicle may consume energy simply holding the attitude that a properly trimmed vehicle maintains with little corrective thrust.

In practical ROV operation, propulsion efficiency, payload integration and tether management are therefore part of battery management.

Domande frequenti

Is a higher Ah rating always better for an underwater drone?

No. Ah only describes charge capacity and cannot be compared properly without voltage. Use watt-hours to compare stored energy, then check weight, dimensions, continuous current, peak current and BMS limits. A larger pack can provide more energy, but its mass and volume may also change buoyancy and vehicle integration. Battery selection should begin with the complete mission power budget.

Can an IP67 battery be installed directly outside an ROV pressure housing?

Not on the basis of IP67 alone. IP67 is an ingress-protection classification rather than a general subsea depth qualification. ROV components must withstand the hydrostatic pressure expected at their operating depth as well as repeated pressure cycles, sealing requirements and the intended environment. A pressure-rated enclosure or other validated subsea battery architecture is therefore required.

Is a LiFePO4 battery suitable for an underwater drone?

A LiFePO4 battery can suit an underwater robot when its voltage, stored energy, discharge capability, BMS, dimensions and mechanical integration match the vehicle. LiFePO4 is particularly relevant where service life and thermal stability are important design priorities. The chemistry alone does not make a battery subsea-ready; the complete enclosure and pressure system still require project-specific engineering.

Does cold water shorten underwater drone battery runtime?

It can. Lower cell temperature can raise internal resistance and reduce available capacity or power in lithium-ion batteries. The effect depends on chemistry, cell design, discharge rate and actual battery temperature, so a fixed percentage should not be applied to every ROV. Cold-water mission estimates should use battery data measured under representative temperature and load conditions.

How much battery reserve should an ROV keep for recovery?

There is no universal reserve percentage suitable for every underwater mission. The margin should account for return distance, surfacing, current, tether conditions, payload use, temperature, battery ageing and possible delays. Commercial and research teams should define the reserve as part of the mission risk assessment rather than treating all nominal battery energy as available working energy.

Conclusione

An underwater drone battery rarely drains quickly because of one component in isolation. Thrusters are normally the largest variable load, but current, tether drag, poor trim, lights, sonar and powered or passive payloads can all change the power required to complete a mission.

The most reliable approach is to build a power budget in watts, convert battery capacity into watt-hours and verify continuous current, peak current, voltage, BMS behaviour and mechanical integration before estimating runtime.

For ROV developers working around 24 V or 48 V architectures, MANLY Battery’s configurable LiFePO4 platforms provide practical starting points for customised robot power systems. The final battery for underwater drone use should then be engineered around the actual mission profile, pressure housing, electrical architecture and recovery requirements rather than selected from capacity alone.

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