18650 battery diameter and length

The 18650 battery is the
gasoline of the 21st century

Working with Battery Bro was such an easy process, and the perfect way to meet our custom power needs!


Alyssa McCarthy

CEO / Mars Rover S&T

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Learn more: What is an 18650 battery?

Why are lithium-ion batteries important?

The world is shifting away from fossil fuels and will one day become fully electric.

Every time the world has harnessed a new generation of energy, be it fire, steam, or diesel, there have been fundamental and broad-stretching improvements to our lives. Battery Bro believes electrical energy stored in batteries will have great implications to the world in the next twenty years as technologies like electric vehicles, smart homes, robotics, and solar power collection are able to reach their full energy potentials.

Lithium-ion is the most promising chemistry of all batteries. Li-ion manufacturers have a regular cycle of improvements, and goals to reach energy density needed for full-adoption seem achievable. Large investments like Tesla’s Gigafactory act as evidence asserting their role as the next generation of batteries to revolutionize energy storage.


Thin, flat sheets of metals comprising the anodes and cathodes of the cell are stacked one on the other, and rolled very tightly together like a jelly-roll. Lithium ions move between these layers, in one direction when the battery is charging, and in the opposite direction when it is discharging.  The tight roll of anodes and cathodes is then jammed into a hard steel cylinder with an open top, and finally capped with the positive pole and sealed. Lithium polymer, or li-po cells on the other hand can be different shapes and are soft and shapeable.


The 18650 (18mm by 65mm) battery is a size classification of lithium-ion batteries. If you have ever held one in your hand, you probably noticed it is the same shape, but a bit larger than a AA battery. AA batteries by comparison are sometimes called 14500 batteries, because they have a 14mm diameter and 50mm height. Cylindrical lithium-ion batteries all follow the same nomenclature, their name being determined by their size (diameter, followed by height). 


The two most important specs for 18650 cells are capacity measured in mAh (milliamp hours) and maximum continuous discharge measured in A (amperes). When selecting a battery type you must favor one over the other. High-capacity batteries have a low max. continuous discharge and high-amp batteries have a low capacity. Typical highest-capacity batteries in 2015 are ~3500mAh, and highest-amp batteries are 30A.


Counterfeit cells are a growing problem, especially prevalent are those from Mainland China and Malaysia where the methods and markets for fake batteries have matured. These batteries often are dangerous and marked with exaggerated specifications. Many used batteries are rewrapped as new and white-labeled. Anti-counterfeiting measures like quality control, and supply-chain inspections are very important for retailers or manufacturers to ensure safety for end-users.


Over 40% of the world’s batteries are lithium-ion. The 18650 battery is one of the most widely produced lithium-ion battery types as it is found in laptops, power-tools, robots, electric vehicles, vaporizers, solar grids, and almost any application you can think of that desires to store electrical energy more efficiently. The cost to manufacture an 18650 has dropped from $10 for ~1500mAh (twenty years ago) to $2 for ~ 3000mAh (today). As cost per kilowatt hour continues to drop, new applications are able to use the technology - fueling demand and economies of scale.


When talking specifically about lithium-ion battery packs, it’s important depending on industry to distinguish between a cell and a battery. A cell becomes a loose, individual 18650 without protection. A battery is then defined as the larger whole: a battery pack composed of many cells with a central PCB (protective circuit) like a BMS (battery management system). Nearly all 18650 cells are sold for assembly into a battery or battery pack. The battery’s protective circuitry has important functions like overcharge protection and load balancing.


Lithium-ion battery chemistry is getting safer every year. Cells are now very sturdy and most people never have problems. However in some circumstances cells malfunction due to mishandling, for example from short-circuiting or puncture. There have also been aircraft crashes because of lithium-ion thermal runaway events (probably initiated by the changes in pressure) - so shipping 18650 batteries by air is getting more difficult.


18650 cells are usually rated at 3.6, 3.7, and sometimes 3.65 volts. These ratings are all essentially the same. It is the average voltage during a complete discharge. The complete voltage range for most 18650s is between 2.5 volts and 4.2 volts. Many people avoid going below 3 volts. Going above or below this range when charging or discharging can result in heat generation, smoke, fire, or explosion.


An 8% improvement to li-ion battery capacity is seen year after year. Compounded, this is slow albeit exponential growth. Within each battery chemistry, improvement is linear. Therefor it takes new generations of batteries with new chemical paradigms (they can all be lithium-ion, with different chemical balances) to allow exponential growth. This growth is expected to continue for at least 25 years, where a physical limit to the amount of energy we can put in a material (~1 eV per atom) may be reached.


Shipping lithium-ion batteries is notoriously difficult, as they are classified as the number one most dangerous good in the world due to their explosive nature on-board airplanes. Packaging and customs regulations are very strict and care has to be made to keep up-to-date with rule changes in multiple countries. Custom battery packs need special UN licensing that costs tens of thousands of dollars to be allowed onboard freight aircraft. Shipping by sea is significantly less regulated but nonetheless still has its challenges and drawbacks.

We curate only the highest-quality cells for our clients.

Why did we create Battery Bro?

A warning about counterfeit 18650 batteries: A significant number of all lithium ion batteries for sale are fake and potentially dangerous, even from well-known sources. Battery Bro solves this problem by providing only verified, tested, and authentic, lithium-ion batteries direct from reputable manufacturers. We found a need for safe, high-quality, wholesale lithium-ion batteries, and that's what we are here to provide.

What is Battery Bro?

  • An American team based in Hong Kong and California, USA.
  • Wholesaler of only authentic, tested, Grade A cells.
  • Focused on honesty, and transparency.
  • Provides custom engineering for battery packs and capacity to supply large 100,000+ cell orders worldwide.


I. Authenticity & Safety Guarantee

Battery Bro only stocks authentic lithium-ion cells that are safe for use in:

  • Electric vehicles - HEV, P-HEV, EV
  • Laptops, smart-phones
  • E-cigarettes, vaporizers, & MODs
  • Powertools, cordless tools, gardening tools
  • Digital cameras, games, MP3 players
  • Shavers, toothbrushes
  • Energy storage both commercial and home
  • Flashlights
  • RC cars, UAVs, drones, quadcoptors
  • Industrial machines, industrial stationary
  • Medical machinery
  • And more...

All batteries are verified and tested and guaranteed genuine before shipping.

II. Only GRADE A cells

  • Grade A: Cells perform to manufacturer specifications.
  • Grade B: Cells under-perform or have other defects.
  • Grade C: Cells are used, repackaged, salvaged, or damaged.

Manufacturers bin their batteries. The A bin is reserved and difficult to obtain. Battery Bro only cells Grade A cells. Many online suppliers sell Grade B cells or lower and do not tell their customers.

III. Fast Shipping & The Lowest Prices

  • Easy Shipping - No customs clearance fees, no hidden shipping fees.
  • International air and sea freight options.
  • The lowest whole sale pricing, cells direct from Asia (China, Hong Kong, Korea, or Japan).

    IV. Battery Bro Platinum Refund

    21-Day Full Refund on all 18650 Batteries. We are committed to the highest quality of service and products.