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21700 vs 18650 Lithium-Ion Batteries Video Review

Milwaukee RedLithium USB Hard Hat Headlamp | 21700 vs 18650

Lithium-Ion Cell Size Fuels Cordless Advancement

Around here, we primarily focus on the tools and gear surrounding the construction industry. That makes the 21700 vs 18650 conversation incredibly relevant to us, but these lithium-ion power sources reach far beyond the latest cordless tools. They’re driving innovation in Teslas, hoverboards, the vaping community, and so much more.

21700 vs 18650: What do the Numbers Mean?

21700, 18650, 20700, and others simply refer to the physical size of the lithium-ion cell. For 18650, it’s an 18 mm diameter x 65 mm length. 21700 is 21 mm x 70 mm. While the explanation is simple, the difference is profound. It’s easy to see with a quick volume calculation.


3.14(9 x 9)(65) = 16,532 cubic mm


3.14(10.5 x 10.5)(70) =  24,233 cubic mm

An extra 5 mm of length and 3 mm of diameter gives us 47% more volume. That’s a little more than 7,700 cubic mm of space to pack with energy-delivering anode, cathode, and electrolyte material.

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Mr Pedantic

Formula for the volume of a cylinder uses RADIUS squared not Diameter squared.


Like the brickies mask, ha ha

Nguyễn Tâm

Cell này rẻ mua ít về đóng pin cho mấy con máy cỏ chơi e Hoàn Hảo 🤪

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