How long will an ESP32 last on a battery in deep sleep?

Let's work out the battery life of a sensor that wakes up, sends data and goes back to sleep. Example: the battery BME280 MQTT sensor.

The formula

Average current = (active current × active time + sleep current × sleep time) / period.

For an ESP32 DevKit waking every 10 minutes:

• active phase with Wi-Fi: ~120 mA × 3 s;
• sleep: ~10 µA for the chip itself — but 10–15 mA on a DevKit because of the USB-UART, the AMS1117 regulator and the power LED!

DevKit:      (120 mA × 3 s + 12 mA × 597 s) / 600 s ≈ 12.5 mA → 2000 mAh ≈ 7 days
Bare module: (120 mA × 3 s + 0.02 mA × 597 s) / 600 s ≈ 0.62 mA → 2000 mAh ≈ 4.5 months

What matters most

1. The board, not the chip. Pick a board with a low-quiescent LDO (ME6211, HT7333) or power the module directly. Desolder the power LED.
2. Wi-Fi connect time. A static IP plus a saved channel and BSSID cut the active phase from 3 s to ~0.5 s.
3. Sensors sleep too. A BME280 in forced mode draws ~0.1 µA between readings; power a DHT22 from a GPIO or through a transistor.
4. The battery voltage divider should use 1 MΩ resistors, not 10 kΩ, or it will drain the cell by itself.

esp_sleep_enable_timer_wakeup(10ULL * 60 * 1000000);  // 10 minutes
esp_deep_sleep_start();

Share your measurements: which board, which battery, how long it lasted.