With the development of electric propulsion technology, underwater thrusters are now widely used in kayaks, small boats, fishing boats, SUPs, remotely operated vehicles (ROVs), and other marine applications.

After purchasing an underwater thruster, many users have two common questions:

“What battery should I use with my underwater thruster?”

“What size ESC (Electronic Speed Controller) do I need?”

The correct battery and ESC selection directly affects:

• Thrust performance

• Runtime

• Operating stability

• Service life

This guide explains how to select the right battery and ESC based on the thruster’s voltage, power, current, and application requirements.

1. What Should You Consider When Choosing a Battery for an Underwater Thruster?

When selecting a battery, the following factors are important:

1. Battery voltage

2. Battery capacity

3. Battery type

4. Maximum discharge capability

1. Battery Voltage Must Match the Thruster Requirements

Common underwater thruster voltage levels include:

• 12V

• 24V

• 36V

• 48V

• 60V

• 72V

Many users assume:

A 24V thruster must use a 24V battery.

However, the more accurate approach is:

The actual operating voltage range of the battery must be within the allowable input voltage range of the thruster.

When selecting a battery, do not only look at the nominal voltage. You also need to consider the battery’s maximum voltage when fully charged.

2. What Is the Difference Between Nominal Voltage and Full-Charge Voltage?

The nominal voltage of a lithium battery represents its rated operating voltage, not its actual maximum voltage.

Lithium-ion Battery (NMC)

Single cell:

• Nominal voltage: 3.7V

• Full-charge voltage: 4.2V

Common configurations:

Battery Configuration	Nominal Voltage	Full-Charge Voltage
3S	11.1V	12.6V
6S	22.2V	25.2V
10S	37V	42V
13S	48.1V	54.6V

LiFePO₄ Battery (Lithium Iron Phosphate)

Single cell:

• Nominal voltage: 3.2V

• Full-charge voltage: 3.65V

Common configurations:

Battery Configuration	Nominal Voltage	Full-Charge Voltage
4S	12.8V	14.6V
8S	25.6V	29.2V
12S	38.4V	43.8V
16S	51.2V	58.4V

Why Is Maximum Voltage Important?

Because the thruster and its controller have a maximum allowable input voltage.

For example:

A 24V underwater thruster:

Allowed input voltage:

20–30V

Then:

✅ 6S lithium-ion battery:

Full voltage 25.2V, suitable.

✅ 8S LiFePO₄ battery:

Full voltage 29.2V, suitable.

However:

If the thruster’s maximum input voltage is only 26V:

❌ 8S LiFePO₄ battery is not recommended.

Therefore:

When selecting a battery, make sure the fully charged battery voltage does not exceed the maximum input voltage of the underwater thruster.

3. Battery Capacity Determines Runtime

Battery capacity is measured in Ah (Amp-hours).

Formula:

Battery Energy (Wh) = Voltage (V) × Capacity (Ah)

Example:

A 24V 100Ah battery:

24 × 100 = 2400Wh

If the thruster power is 900W:

Theoretical full-power runtime:

2400 ÷ 900 ≈ 2.6 hours

Actual runtime will be affected by:

• Boat weight

• Water current

• Wind and waves

• Speed

• Motor efficiency

• Battery losses

Recommended Battery Capacity for Different Applications

The following runtime estimates are based on typical underwater thruster applications.

Application	Recommended Battery Capacity	Continuous Full Throttle	Normal Cruising
Short recreational use / testing	24V 30–50Ah	About 0.5–1 hour	About 1–2 hours
Fishing / kayak cruising	24V 50–100Ah	About 1–2 hours	About 3–5 hours
Long-distance cruising	24V 100Ah+	About 2+ hours	About 5+ hours
High-power boat propulsion	48V 100Ah+	About 2+ hours	About 4–6 hours

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Why Is Cruising Runtime Much Longer Than Full-Throttle Runtime?

At full throttle, the thruster continuously operates at maximum power.

For example:

A 1000W thruster:

At full throttle:

Power consumption is close to 1000W.

However, during normal operation:

• Users usually do not run at full throttle continuously

• Speed is adjusted according to water conditions

• Acceleration is intermittent

The average power consumption may only be 40–60% of the maximum power.

Therefore:

Cruising runtime can often be 2–3 times longer than continuous full-throttle operation.

4. Choosing the Right Battery Type

LiFePO₄ Battery (Lithium Iron Phosphate)

Advantages:

✔ High safety
✔ Long cycle life
✔ Stable discharge performance
✔ Suitable for marine environments

Suitable for:

• Kayaks

• Fishing boats

• Small boats

• Long-duration cruising

Lithium-ion Battery (NMC)

Advantages:

✔ Higher energy density
✔ Lighter weight
✔ Strong power output capability

Suitable for:

• Weight-sensitive applications

• High-performance systems

Note:

A reliable BMS (Battery Management System) is required.

2. How to Choose an ESC for an Underwater Thruster?

An ESC (Electronic Speed Controller) is responsible for:

• Controlling motor speed

• Adjusting output power

• Protecting the motor and electrical system

When selecting an ESC, consider:

1. Voltage range

2. Maximum continuous current

3. Motor type

1. Select the ESC Based on Maximum Motor Current

Recommended principle:

ESC continuous current rating ≥ Motor maximum operating current × 1.2–1.5

Example:

Motor maximum operating current:

50A

Recommended:

60–75A or higher ESC.

This helps reduce:

• Heat buildup during continuous operation

• ESC overload

• Reduced service life

ESC Selection Reference

Maximum Motor Current	Recommended ESC
≤20A	30A ESC
30–40A	50A ESC
50–60A	80–100A ESC
80–100A	120–150A ESC
120A+	150A+ ESC

2. Confirm the Motor Type

Most underwater thrusters use:

Brushless Three-Phase Motor (BLDC)

Features:

• Three power wires

• Requires a three-phase brushless ESC

• Usually controlled by PWM signal

Connection:

Battery
 ↓
ESC
 ↓
Brushless Motor

3. What Is the Difference Between PWM ESC and FOC ESC?

PWM ESC

Advantages:

✔ Lower cost
✔ Good compatibility
✔ Widely used

Suitable for:

• Standard underwater thrusters

• Auxiliary boat propulsion

• DIY projects

FOC ESC

FOC (Field-Oriented Control) is a more advanced motor control technology.

Advantages:

✔ Quieter operation
✔ Smoother low-speed control
✔ Higher efficiency
✔ Lower heat generation

Suitable for:

• ROV systems

• Marine propulsion systems

• Long-duration applications

Important:

FOC ESCs require proper matching with motor parameters.

Incorrect settings may cause:

• Startup failure

• Motor vibration

• Reduced efficiency

3. What Parameters Should You Confirm Before Purchasing?

Before purchasing an underwater thruster, battery, or ESC, confirm:

• ✔ Thruster operating voltage range

• ✔ Maximum allowable input voltage

• ✔ Maximum power

• ✔ Maximum operating current

• ✔ Whether the ESC is built-in

• ✔ Motor type

• ✔ Required battery capacity

• ✔ Expected runtime

Summary

When selecting a battery and ESC for an underwater thruster, remember:

Battery Selection:

The battery voltage must match the thruster requirements, the full-charge voltage must not exceed the maximum input voltage, and battery capacity determines runtime.

ESC Selection:

The ESC voltage rating must match the system, and the continuous current rating should include a 20–50% safety margin.

For most kayak, small boat, and fishing applications:

LiFePO₄ battery + a properly sized brushless ESC

is usually a safe, stable, and long-lasting solution.