What Size Is a 650 Battery?

A “650 battery” is a cylindrical lithium‑ion cell that is approximately 18 mm in diameter and 65 mm in length (commonly referred to as 18650), with variations in capacity and exact dimensions depending on the manufacturer. In practice, most people saying “650 battery” are referring to the 18650 format, a long‑standing standard in flashlights, laptops, power tools, and older vape devices.

Understanding the “650” Battery Designation

The term “650 battery” on its own is technically incomplete. It is shorthand used in many enthusiast and hobbyist communities to mean an 18650 cell, but battery sizes are usually described with four or five digits, not just “650.” Those numbers encode the cell’s diameter and length in millimeters, plus a trailing zero indicating a cylindrical shape.

How the Numbering System Works

If you encounter an 18650, 21700, or 26650 battery, all of those numbers follow the same basic convention. The first two digits are the approximate diameter in millimeters, the next two digits are the approximate length, and the final “0” means it is a cylindrical cell. So when someone says “650 battery,” they usually mean that last part of the code — the 65.0 mm length — while omitting the diameter.

The following list details the standard interpretation of common cylindrical lithium‑ion battery codes so it’s clear where “650” fits in.

• 18650 – about 18 mm diameter, 65 mm length, 0 = cylindrical cell
• 21700 – about 21 mm diameter, 70 mm length, 0 = cylindrical cell
• 26650 – about 26 mm diameter, 65 mm length, 0 = cylindrical cell
• 14500 – about 14 mm diameter, 50 mm length, 0 = cylindrical cell
• 16340 – about 16 mm diameter, 34 mm length, 0 = cylindrical cell

This pattern shows why “650” is insufficient by itself: it only reflects the length (65 mm) and the cylindrical form, not the diameter, which is essential for compatibility.

So What Size Is a “650 Battery” in Practice?

In everyday usage, a “650 battery” almost always means an 18650 cell. That is the dominant 65 mm‑long format and has become a de‑facto standard in many industries.

Typical Physical Dimensions of an 18650 Battery

Manufacturers and standards bodies specify a nominal size, but real‑world cells vary slightly due to casing, safety vents, and the presence of protection circuits. Still, they tend to fall within predictable ranges.

The list below shows the typical physical measurements of a standard 18650 cell and how those values can shift depending on design features.

• Nominal diameter: 18 mm (usually about 18.0–18.6 mm in practice)
• Nominal length: 65 mm (typically about 64.8–65.3 mm for bare cells)
• Button‑top or protected cells: can extend to roughly 66–69 mm in length
• Shape: cylindrical
• Typical chemistry: Li‑ion variations such as NMC, NCA, or INR (exact chemistry varies by maker)

These modest variations mean that while an 18650 cell is “65 mm long” in name, a protected or button‑top version may not fit into very tight battery compartments designed only for bare flat‑top cells.

Other “650” Format Batteries: 26650 and Beyond

Not every cell ending in “650” is an 18650. The length may be the same 65 mm, but a different diameter creates a very different battery. For devices with roomier compartments or higher current demands, other 65 mm‑long options exist.

26650 Batteries

Among the larger formats, the 26650 is the best‑known alternative to the 18650. It offers a wider body, allowing for higher capacity and current in a single cell, at the cost of size and weight.

The following list outlines the key dimensional characteristics of a 26650 cell for comparison with 18650.

• Nominal diameter: 26 mm (often around 26.0–26.5 mm)
• Nominal length: 65 mm (commonly 65–66 mm, longer if protected/button‑top)
• Shape: cylindrical
• Typical use cases: high‑power flashlights, some power tools, and custom battery packs

This contrast shows why specifying the full code (18650 vs 26650) matters: a 26650 will not fit into most housings designed around the slimmer 18650 format, even though both are “65 mm‑length” cells.

Why the Exact Size Matters

Beyond a rough measurement, the precise size of a 650‑series battery affects safety, reliability, and physical compatibility. Using the wrong format or forcing a tight fit can damage devices or compromise electrical contact, especially in high‑current applications.

Fit, Compatibility, and Safety Considerations

Different devices are engineered around specific cell formats, including the type of positive terminal, the length of the cell, and how springs or contacts compress. Understanding the size ranges for 65 mm‑class batteries helps consumers and technicians avoid costly mistakes.

The following list summarizes the main factors to check when selecting or replacing a 650‑series lithium‑ion cell.

• Diameter compatibility: Ensure the battery compartment is built for 18 mm (18650) or 26 mm (26650), not just any “650.”
• Length tolerances: Some tight devices only accept bare flat‑top cells; protected or button‑top cells may be too long.
• Terminal style: Flat‑top vs button‑top can affect whether proper contact is made in series or single‑cell holders.
• Chemistry and discharge rating: Even if the size is correct, you must match voltage (usually 3.6–3.7 V nominal) and current requirements.
• Protected vs unprotected: Protected cells add length but include safety electronics (over‑charge, over‑discharge, and short‑circuit protection).

Taking these factors into account prevents misfits and reduces the risk of overheating, venting, or device damage, especially in high‑drain uses like vaping, e‑bikes, or powerful LED flashlights.

Common Uses for 18650 and Other 650‑Series Cells

The dominance of the 18650 format has made it a workhorse cell in both consumer electronics and industrial applications, even as newer sizes like 21700 and 4680 gain ground in electric vehicles and energy storage. Understanding typical use cases further clarifies what most people mean when they reference a “650 battery.”

Devices That Commonly Use 18650 Batteries

The reach of the 18650 extends from legacy consumer gear to modern hobbyist hardware. While many new products have switched to other formats or custom packs, 18650 cells remain widely used and readily available.

The following list highlights some of the most common categories of devices that rely on 18650‑class batteries.

• Flashlights and headlamps: Particularly higher‑output LED models requiring sustained current.
• Laptop battery packs (older generations): Many traditional “brick” laptop batteries contained multiple 18650 cells in series and parallel.
• Vape mods / e‑cigarette devices (legacy and enthusiast gear): Single or dual‑cell setups often specified high‑drain 18650 cells.
• Power banks and DIY energy storage: Hobbyist power walls and USB battery packs commonly use reclaimed or new 18650 cells.
• Electric tools and hobby projects: Some cordless tools, e‑bike packs, and robotics projects rely on 18650 arrays.

This wide adoption is the main reason “650 battery” has become informal shorthand for 18650: in many everyday contexts, it is simply the most common 65 mm‑long cylindrical cell in circulation.

Summary

When someone asks, “What size is a 650 battery?” they are almost always referring to an 18650 lithium‑ion cell, which is approximately 18 mm in diameter and 65 mm in length. The “650” part of the code indicates a 65 mm‑long cylindrical cell, but the first digits (such as 18 or 26) are crucial to define the diameter and ensure a proper fit. Variants like the larger 26650 (26 mm × 65 mm) share the same length but are not interchangeable with 18650 cells. For safe and reliable use, it’s essential to specify and confirm the full battery designation—18650, 26650, or another exact format—rather than relying on “650” alone.

Can am outlander 650 battery size?

The common battery size for a Can-Am Outlander 650 is a 12V, 18-20Ah, 250-310 CCA battery, with the YTX20L-BS or RG20L-BS part number being frequently cited. For an exact fit, it’s best to confirm the battery’s dimensions (approximately L=6.89cap L equals 6.89𝐿=6.89, W=3.43cap W equals 3.43𝑊=3.43, H=6.14cap H equals 6.14𝐻=6.14 inches) and the terminal configuration with your specific model year.
 
Key specifications

• Voltage: 12V
• Capacity: 18-20Ah
• Cold Cranking Amps (CCA): 250-310 CCA
• Common part numbers: YTX20L-BS, RG20L-BS, or BTX20L-BS 

How to confirm the correct battery

• Check your owner’s manual: This is the most reliable source for the exact specifications for your model year. 
• Look at the current battery: Check for a label on the existing battery for its part number and specifications. 
• Measure the physical space: Measure the length, width, and height of the battery compartment to ensure a physical fit. 

What is a group 65 battery?

A group 65 battery is a specific size standard (BCI) for a 12-volt lead-acid or AGM automotive battery, measuring approximately 12×7.5×7.512 cross 7.5 cross 7.512×7.5×7.5 inches. It is commonly used in vehicles like trucks, SUVs, and cars, offering strong starting power, particularly in cold weather, with typical cold cranking amp (CCA) ratings between 650 and 950. These batteries are often maintenance-free and have a right-side positive terminal for easier installation.
 
Key characteristics

• Dimensions: Approximately 121212 inches long, 7.57.57.5 inches wide, and 7.57.57.5 inches high. 
• Voltage: 12 volts. 
• Power: Typically rated between 650 and 950 CCA, ensuring reliable engine starts in cold conditions. 
• Reserve Capacity: Ranges from 120 to 150 minutes, indicating how long the battery can run at a consistent level. 
• Terminal: Has a right-side positive terminal for straightforward installation. 
• Chemistry: Available as standard flooded lead-acid or absorbed glass mat (AGM) types. 
• Common Applications: Used in a wide variety of vehicles including Ford, Dodge, Chrysler, Jeep, trucks, and SUVs. 

What size is a 650 car battery?

The 650CR is engineered with dimensions of 303mm length, 174mm width, and 220mm O/A height to ensure a secure fit in your vehicle. Despite its immense power, it weighs just 23.17kg, providing a power-to-weight ratio that ensures optimal performance.

What does 650 mean on a car battery?

Cold Cranking Amps Rating
Cold cranking amps (CCA), such as 650 CCA, is an industry standard measure of how much power a battery can provide at zero degrees Fahrenheit.