Around here, we primarily focus on the tools and gear surrounding the construction industry. That makes the 21700 vs 18650 lithium-ion battery cell conversations incredibly relevant to us. After all, 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 materials.