Battery Knowledge2026-07-07 · 7 min read
26650 vs 21700 Battery: Which Cell Format Should You Choose?
Compare 26650 and 21700 lithium cells by size, capacity, energy density, pack layout and typical applications for OEM battery design.
DC
Written by Daniel Chen
Senior Battery Systems Engineer · BLUS ENERGY R&D
Technically reviewed by BLUS ENERGY R&D Team
Both 26650 and 21700 are cylindrical lithium battery formats, but they serve different design priorities. 21700 cells are popular in modern high-energy packs because they balance capacity, size and assembly efficiency. 26650 cells are larger and may be selected where the mechanical design already supports the wider diameter.
Size and capacity comparison
| Cell format | Approx. size | Common capacity range | Design note |
|---|---|---|---|
| 21700 | 21mm diameter x 70mm height | 3,000mAh to 5,000mAh | Strong choice for compact high-energy packs |
| 26650 | 26mm diameter x 65mm height | 4,000mAh to 6,000mAh | Larger diameter, useful when pack space allows |
When 21700 is usually better
For many new OEM projects, 21700 is easier to package because it offers high capacity per cell while keeping the pack narrower than 26650. It can reduce the number of cells, welds and balancing points compared with smaller 18650 designs.
When 26650 can still make sense
26650 can work well when the enclosure has enough diameter clearance, the design already uses this format, or the customer wants a specific supplier ecosystem. The trade-off is a wider cell that may limit compact pack layout.
For most new cylindrical lithium battery projects, BLUS ENERGY usually evaluates 18650, 21700 and application-specific alternatives together. See our cylindrical lithium battery pack page for custom pack options.
Frequently asked questions
Is 26650 bigger than 21700?+
Yes. A 26650 cell is about 26mm in diameter and 65mm tall, while a 21700 cell is about 21mm in diameter and 70mm tall.
Does 26650 have more capacity than 21700?+
It can, but not always. Capacity depends on cell chemistry, supplier and grade. Modern 21700 cells can reach high capacity while remaining easier to package.
Which is better for custom battery packs?+
21700 is often better for new compact high-energy designs, while 26650 may be useful when the enclosure already supports the wider format.
