Xtar INR18650 2600mAh (Cyan) 2020
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Official specifications:
- Nominal capacity: 2600mAh
- Nominal voltage: 3.6V
- End of discharge voltage: 2.5V
- Max. pulse discharge current: 35A
- Max. continuous discharge current: 25A
- Charging temperature range: 0°C ~ 60°C
- Discharging temperature range: -40°C ~60°C
- Cycle life: 500 cycles
- Internal resistance <20mOhm
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This is high current cells with fairly low capacity.
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%202020/Xtar%20INR18650%202600mAh%20(Cyan)%202020-Capacity.png)
The two cells do not match, the A cell has lower capacity and handles less current. I stop the test a bit early at high current due to the cell temperature.
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%202020/Xtar%20INR18650%202600mAh%20(Cyan)%202020-Temp-30.0.png)
%202020/Xtar%20INR18650%202600mAh%20(Cyan)%202020-CapacityTimeHours.png)
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%202020/Xtar%20INR18650%202600mAh%20(Cyan)%202020-Charge.png)
With these charge curves it looks like one of the cells are faulty.

Conclusion
One of the cells looks fairly good, the other do not.
This makes these cells a bad choice.
Notes and links
The batteries was supplied by Xtar for review.
How is the test done and how to read the charts
How is a protected LiIon battery constructed
More about button top and flat top batteries
Graphical comparison to 18650 and other batteries
Table with all tested LiIon batteries