I would like to calculate the battery runtime for an ESP32, using a 18650 battery with 2600 mAh (Datasheet).

When I am using a calculator such as this one, it requires me to put in a discharge safety value. How can I get/calculate that?

Using the battery I have right now, the cutoff voltage is around 3 V (from experience) and I can charge the battery up to 4.2 V. But how would I get the % value?

The ESP is sending some sensor data via LoRa and will then go to (deep) sleep:

Mode Avg. Consumption Duration
Deep Sleep ~ 6.4 µA 300s
Up ~ 4.1 mA 20s

Thanks & BR!

  • \$\begingroup\$ At what current(s) are you draining the battery? Is it a constant current or variable? How bad is it if the equipment shuts itself off (on a scale of "my desk light goes out" to "my heart stops"). Please edit your question with these details. \$\endgroup\$
    – TimWescott
    Dec 3, 2022 at 20:09

1 Answer 1


You can get that value from the characteristic discharge curves of the battery, as seen on page 5 of the datasheet you linked: At low discharge rate (0.5A), the cell will reach 3V after 2400mAh have been drained from it. That's 92.3% of the cell's nominal capacity, with 7.7% (200mAh) of the stored charge remaining in the cell.


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