Squeezing Months From an ESP32 Coin Cell

A datasheet promises microamps in deep sleep. The bench rarely agrees, because the chip is only part of the board.

Where the current actually goes

• Onboard regulators and USB-serial chips idle in the milliamp range. On a custom board, leave them off the BOM; on a dev board, you cannot win.
• GPIO with floating inputs leak. Pull everything to a defined state before esp_deep_sleep_start().
• Wi-Fi association is the budget killer. Associating costs far more than the payload — batch readings and send bursts.

// Hold critical pins through sleep so peripherals don't float and draw current.
gpio_hold_en(SENSOR_POWER_PIN);
gpio_deep_sleep_hold_en();
esp_deep_sleep_start();

A rule of thumb

Optimize the wake before the sleep. A 30µA sleep current is irrelevant if you wake for 4 seconds to negotiate Wi-Fi every minute.

Measure with a current shunt across a real cell, not a bench supply — internal resistance changes everything once the battery is half-drained.