RTC memory persistence requirements

[majvan]

Hello.

I have a code which uses RTC memory during deep sleep. The code works all right when I power my NodeMCU ESP32 via USB cable (+5V).
However, when I use a battery which powers directly via +3V3 (actual voltage is +3V), the core works, the RTC timer wakes up, but the RTC data is reset to zero, i.e. it does not preserve the values.

Anybody experienced the same? Is there any electrical characteristics / table for the RTC RAM retention?

[ESP_Sprite]

Those subsystems work well under 3V, so I think the reason is that your ESP32 resets somewhere along the way. Check the reset reason at the start of your program output, if that isn't some wake from sleep, the RTC memory gets zeroed.