What Is 21700 battery

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Last updated: April 15, 2026

Quick Answer: The 21700 battery is a lithium-ion cell measuring 21mm in diameter and 70mm in length, introduced in 2017 by Panasonic for use in Tesla's Model 3. It offers higher capacity and energy density than older 18650 cells, typically storing 3,000–5,000mAh at 3.6–3.7 volts.

Key Facts

The 21700 battery has a diameter of 21mm and length of 70mm.
Introduced commercially in 2017 by Panasonic for Tesla vehicles.
Typical capacity ranges from 3,000mAh to 5,000mAh.
Operates at a nominal voltage of 3.6–3.7 volts.
Offers 20–30% higher energy density than 18650 batteries.

Overview

The 21700 battery is a lithium-ion rechargeable cell that emerged as a successor to the widely used 18650 format. With dimensions of 21mm in diameter and 70mm in length, it provides greater energy storage in a slightly larger form factor, making it ideal for high-drain applications like electric vehicles and advanced flashlights.

First mass-produced in 2017, the 21700 was developed through a collaboration between Panasonic and Tesla for use in the Model 3. Its design allows for improved thermal management and higher capacity, addressing limitations of older cylindrical cells. As demand for longer-lasting, more efficient power sources grows, the 21700 has become a preferred choice across industries.

Size: Measures exactly 21mm in diameter and 70mm long, making it larger than the 18650 but still compact enough for portable devices.
Capacity: Typically stores between 3,000mAh and 5,000mAh, with high-end models like the Samsung 50S reaching up to 5,000mAh.
Voltage: Operates at a nominal voltage of 3.6 to 3.7 volts, with a maximum charge voltage of 4.2 volts per cell.
Energy Density: Offers approximately 250–300 Wh/kg, a 20–30% improvement over standard 18650 batteries.
Applications: Used in electric vehicles, vapes, flashlights, power tools, and solar energy storage systems due to its high power output and reliability.

How It Works

The 21700 battery operates on lithium-ion chemistry principles, where lithium ions move between the anode and cathode during charge and discharge cycles. Its larger size allows for increased electrode surface area, enhancing ion flow and reducing internal resistance, which improves efficiency and lifespan.

Electrode Design: Uses a high-nickel NMC (Nickel Manganese Cobalt) cathode that boosts energy density and reduces reliance on cobalt, lowering cost and environmental impact.
Internal Structure: Features a single jellyroll configuration that maximizes space utilization and minimizes heat buildup during high-current discharge.
Thermal Management: Incorporates advanced thermal runaway protection mechanisms, including pressure relief vents and ceramic-coated separators.
Charging Mechanism: Requires a constant-current/constant-voltage (CC/CV) charging method, typically reaching full charge in 2–3 hours with a compatible charger.
Discharge Rate: Supports continuous discharge currents of up to 20–35 amps, suitable for high-power devices like e-bikes and power tools.
Lifespan: Rated for 500–1,000 charge cycles before capacity drops below 80%, depending on usage and charging habits.

Comparison at a Glance

Below is a detailed comparison of the 21700 with other common lithium-ion cylindrical cells:

Model	Diameter (mm)	Length (mm)	Typical Capacity (mAh)	Energy Density (Wh/kg)
21700	21	70	3,000–5,000	250–300
18650	18	65	2,200–3,500	200–250
20700	20	70	2,800–3,800	230–270
26650	26	65	3,000–5,500	220–260
32650	32	65	4,500–6,500	200–240

The 21700 strikes a balance between size and performance, offering higher energy density than the 18650 and 20700 while remaining more compact than the 26650 and 32650. Its optimized design makes it particularly effective in space-constrained, high-power applications like EVs and portable electronics, where efficiency and safety are critical.

Why It Matters

The 21700 battery represents a significant advancement in portable energy technology, enabling longer runtimes and faster charging across multiple industries. Its adoption in Tesla vehicles has driven mass production, reducing costs and accelerating innovation in battery chemistry and packaging.

Electric Vehicles: Powers Tesla’s Model 3 and Model Y, contributing to increased range and reduced battery pack weight compared to previous models.
Consumer Electronics: Used in high-performance flashlights and vapes, where longer runtime and stable voltage output are essential.
Renewable Energy: Integrated into solar power storage systems, allowing efficient energy retention and discharge over extended periods.
Industrial Tools: Enables cordless power tools to operate at higher torque and longer durations without frequent recharging.
Environmental Impact: Reduces reliance on cobalt through nickel-rich cathodes, leading to lower environmental and ethical concerns in mining.
Market Growth: Global 21700 battery market is projected to grow at over 15% CAGR from 2023 to 2030, driven by EV and energy storage demand.

As battery technology evolves, the 21700 sets a new standard for performance, safety, and scalability. Its widespread adoption signals a shift toward more efficient, sustainable energy solutions across transportation, consumer goods, and infrastructure.