A robot is only as good as its power system. Motors, motor drivers, servos, Raspberry Pi boards, sensors, cameras and communication modules all depend on a stable and appropriately sized power source.

Choosing a battery for a robot is therefore not simply a matter of picking the highest-capacity battery. You need to consider voltage, current, weight, runtime, motor loads, discharge characteristics, charging requirements and safety.

For example, Pololu's robot platforms use different battery approaches depending on the robot: its Zumo robots can use rechargeable NiMH cells, while its documentation also emphasizes matching the power source to motor and controller requirements.

🤖 Why Batteries Matter So Much in Robotics

A typical mobile robot may have several different power requirements:

Battery → Power Distribution → Motor Driver → Motors

and simultaneously:

Battery → Voltage Regulator → Raspberry Pi / Arduino / Sensors

The motors can create large changes in current demand, especially when:

• Starting from rest
• Climbing an incline
• Carrying a load
• Turning on high-friction surfaces
• Reaching stall conditions

Meanwhile, the electronics require relatively stable voltage.

This is why many robots use separate regulated power rails for motors and electronics. Pololu's 3pi, for example, uses power-management circuitry to provide regulated power to different parts of the robot.

🔋 1. LiPo Batteries

Lithium Polymer (LiPo) batteries are one of the most popular choices for high-performance robotics.

They are especially useful when a robot needs:

• High current
• Low weight
• High power-to-weight ratio
• Compact packaging
• Rapid acceleration

Common robotics applications

• RC robots
• Combat robots
• Drones
• Autonomous vehicles
• Robotic arms
• High-speed wheeled robots
• Quadruped robots

Example: 3S LiPo

A 3S LiPo contains three cells connected in series.

Nominal voltage:

3 × 3.7 V ≈ 11.1 V

Fully charged:

≈ 12.6 V

A common robotics battery might be:

11.1 V, 2200 mAh, 30C

Theoretical current capability based on the C-rating:

2.2 Ah × 30C = 66 A

The actual permissible current depends on the manufacturer's specifications and operating conditions.

Advantages

• Very high power-to-weight ratio
• High discharge capability
• Lightweight
• Compact
• Excellent for motor-driven robots

Disadvantages

• Requires careful charging
• Requires appropriate protection
• Over-discharge can damage the pack
• Physical damage can be hazardous
• Requires appropriate storage and handling

Best for: High-performance mobile robots, drones, RC robots and robots requiring high motor current.

🔋 2. Li-ion Batteries

Lithium-ion batteries are extremely common in robotics because they provide a good combination of:

Energy density + weight + availability + cost

Common cells include:

• 18650
• 21700
• Li-ion pouch cells

Robotics applications

• Autonomous mobile robots
• Raspberry Pi robots
• Delivery robots
• Educational robots
• Inspection robots
• Service robots
• Robot vacuum cleaners

Li-ion is particularly useful when long runtime matters more than extreme peak power.

Example

A robot using a 4S Li-ion pack might have:

14.8 V nominal

The exact voltage depends on the cell chemistry and pack configuration.

Advantages

• High energy density
• Relatively lightweight
• Good runtime
• Easy to build into custom battery packs
• Widely available

Disadvantages

• Requires proper protection
• Cell balancing may be required in multi-cell packs
• High-current capability varies significantly between cells

Best for: General-purpose autonomous robots where runtime and weight are important.

🔋 3. LiFePO₄ Batteries

Lithium Iron Phosphate (LiFePO₄ or LFP) is particularly interesting for robots that need long service life and robust operation.

Its nominal cell voltage is around 3.2–3.3 V, lower than many conventional Li-ion chemistries.

Robotics applications

• Industrial mobile robots
• AGVs
• AMRs
• Heavy-duty robots
• Outdoor robots
• Autonomous vehicles
• Long-running educational platforms

Advantages

• Long cycle life
• Good thermal stability
• Good high-current capability
• Robust chemistry
• Well suited to repeated charging/discharging

Disadvantages

• Heavier/larger for the same energy compared with some high-energy-density Li-ion systems
• Higher initial cost in some applications

LiFePO₄ is often an excellent choice when reliability and cycle life matter more than minimizing weight.

🔋 4. NiMH Batteries

Nickel-Metal Hydride (NiMH) batteries are still extremely useful for small educational and hobby robots.

A standard NiMH cell has a nominal voltage of approximately 1.2 V.

For example:

4 × AA NiMH = 4.8 V nominal

This is exactly the type of arrangement recommended by Pololu for several of its small robots.

Applications

• Line-following robots
• Arduino robots
• STEM kits
• Small wheeled robots
• Educational platforms
• Beginner robotics projects

Advantages

• Rechargeable
• Easy to use
• Available in standard AA/AAA formats
• Relatively forgiving
• No special lithium pack construction required

Disadvantages

• Heavier than lithium batteries for equivalent energy
• Lower energy density
• Lower voltage per cell

Best for: School robotics, Arduino robots and beginner platforms.

🔋 5. Lead-Acid Batteries

Lead-acid batteries are heavy, but they remain useful when weight is less important than cost and ruggedness.

Robotics applications

• Large AGVs
• Heavy robots
• Industrial prototypes
• Outdoor robotic platforms
• Backup power systems

A common configuration is:

12 V lead-acid battery

Advantages

• Low cost
• High surge current
• Easy availability
• Mature technology

Disadvantages

• Very heavy
• Large physical size
• Lower energy density

Best for: Large/heavy robots where battery weight isn't a major limitation.

🔋 6. Alkaline Batteries

Alkaline batteries are generally not the first choice for serious robotics, but they are useful for demonstrations and simple educational projects.

A typical alkaline cell is around 1.5 V nominal.

Applications

• Simple STEM kits
• Basic line followers
• Small educational robots
• Testing prototypes

Problem for robotics

Motors can draw significant current, particularly during startup. Ordinary alkaline cells are often a poor choice for high-current motor applications. Pololu specifically notes that alkaline cells are typically poor choices for high-current applications.

⚡ Battery Comparison for Robotics

These are broad practical comparisons, not universal ratings; actual performance depends heavily on the specific cell/pack.

🔌 Battery Voltage: The First Thing to Check

Before buying a battery, check your robot's electronics.

Suppose your robot uses:

12 V motors

That does not automatically mean you should connect any 12 V battery directly to the motor driver.

You need to check:

1. Motor voltage
2. Motor-driver voltage range
3. Motor-driver current rating
4. Battery's fully charged voltage
5. Controller voltage
6. Regulator input range

This is particularly important with lithium batteries because their fully charged voltage is higher than their nominal voltage.

For example:

3S LiPo

Nominal: 11.1 V
Fully charged: 12.6 V

A device rated close to 12 V may therefore require careful checking before a 3S LiPo is connected.

Pololu specifically warns that a nominal 11.1 V three-cell lithium battery can measure well above 12 V when fully charged, and therefore may not be appropriate for some robot electronics.

⚙️ Battery Capacity: mAh vs Runtime

A common mistake is thinking:

"A 5000mAh battery will always last twice as long as a 2500mAh battery."

Not necessarily.

Battery energy is better compared using watt-hours (Wh):

Energy ≈ Voltage × Capacity (Ah)

For example:

Battery A

11.1 V × 2.2 Ah

≈ 24.4 Wh

Battery B

7.4 V × 5 Ah

≈ 37 Wh

Even though Battery B has a lower voltage, it stores more energy.

Therefore, when comparing different battery packs, Wh is often more useful than mAh alone.

🤖 Motor Current Is Critical

A robot may consume relatively little current while cruising but many times more current when the motors start or stall.

Consider a robot with two DC motors.

If each motor can draw:

5 A

then the motor system could potentially demand:

5 A + 5 A = 10 A

And the actual peak can be higher depending on the motor and mechanical load.

Therefore, selecting a battery solely based on capacity is a mistake.

You need to consider:

Battery → Motor Driver → Motor

The entire chain must be capable of handling the required current.

🧠 Don't Power Everything Directly From the Battery

A good robotics power architecture often looks like this:

              BATTERY
                 │
          ┌──────┴──────┐
          │             │
     MOTOR DRIVER    DC-DC REGULATOR
          │             │
       MOTORS       ┌───┴────┐
                    │        │
                  5V/6V    3.3V
                    │        │
                 Raspberry  Sensors
                    Pi
                 Arduino

This separation is extremely useful because motors can generate electrical noise and cause voltage disturbances.

For example, Pololu's 3pi uses different regulated power paths for motors and logic rather than simply feeding the battery voltage everywhere.

🔋 What Battery Should You Choose?

🟢 Arduino Line-Following Robot

Recommended: 4×AA NiMH

Simple, inexpensive and easy to replace.

🟢 Raspberry Pi Robot Car

Recommended: Li-ion or LiPo + appropriate DC-DC regulation

Don't connect a random lithium pack directly to the Raspberry Pi.

🟢 High-Speed Robot

Recommended: LiPo

The high discharge capability and low weight make LiPo particularly attractive.

🟢 Quadruped Robot

Recommended: High-current LiPo or suitable Li-ion/LiFePO₄ pack

The battery must handle the combined load of multiple motors/servos.

🟢 Industrial AMR / AGV

Recommended: LiFePO₄ or industrial Li-ion

Here, cycle life, safety, runtime and reliability may be more important than minimum weight.

🟢 School STEM Robot

Recommended: NiMH or alkaline for very simple designs

Rechargeable NiMH is generally preferable if the robot will be used repeatedly.

🔥 LiPo vs Li-ion for Robotics

This is one of the most important comparisons for robot builders.

If your priority is:

POWER → LiPo

If your priority is:

RUNTIME → Li-ion

If your priority is:

LONG LIFE + ROBUSTNESS → LiFePO₄

If your priority is:

SIMPLICITY → NiMH

🛡️ BMS and Battery Protection

Lithium battery packs need appropriate protection and management.

Depending on the battery design, a BMS can provide functions such as:

• Overcharge protection
• Over-discharge protection
• Over-current protection
• Short-circuit protection
• Cell balancing
• Temperature monitoring

But a BMS does not make an incorrectly designed battery system safe by itself.

The charger, battery cells, wiring, connectors, fuse, motor driver and BMS all need to be appropriate for the application.

⚠️ Common Battery Mistakes in Robotics

❌ Choosing only by mAh

A higher mAh rating doesn't necessarily mean the battery can supply enough current.

❌ Ignoring fully charged voltage

A "12 V" lithium battery can have a substantially higher voltage when fully charged.

❌ Connecting a Raspberry Pi directly to a random battery

The Pi requires an appropriate regulated supply.

❌ Ignoring motor stall current

A robot can draw dramatically more current when its wheels are blocked.

❌ Using an unsuitable charger

Different chemistries require different charging methods.

❌ Forgetting a fuse

A short circuit in a high-current battery pack can be extremely dangerous.

❌ Using undersized wires

High-current robot systems require appropriately sized wiring and connectors.

🏆 The Best Battery Depends on the Robot

There is no universal "best robotics battery."

Think of the choice this way:

Small educational robot → NiMH

Fast mobile robot → LiPo

Autonomous robot → Li-ion

Heavy-duty robot → LiFePO₄

Large low-cost platform → Lead-acid

The right battery is the one that can safely provide the required voltage, current and energy while meeting the robot's weight, size, runtime and charging requirements.

🔧 Final Checklist for Robot Builders

Before selecting a battery, answer these questions:

1. What voltage do my motors require?

2. What voltage does my motor driver accept?

3. What is the motor's running current?

4. What is the motor's stall current?

5. How much current can the battery safely deliver?

6. How much runtime do I need?

7. What is the maximum acceptable battery weight?

8. Do I need a BMS?

9. What charger does the battery require?

10. Do my Raspberry Pi/Arduino/sensors need a separate regulator?

If you answer those ten questions, you can usually narrow down the right battery chemistry and pack configuration for your robot.