operating voltage

[obod0002]

with the various models of the ESP chips we also notice varying voltage ranges, e.g.

ESP-WROOM-02: Operating voltage 2.7V ~ 3.6V
ESP8266EX: Operating Voltage 2.5V ~ 3.6V
ESP32-WROVER: Operating voltage/Power supply 2.3 V ~ 3.6 V
(taken from the officials datasheets)

At the moment I'm using LiFePO4's, so I don't need any LDO.
With reduced voltages for a safe operation I might also consider a boost converter using just one or two alkaline non-rechargables (at the moment one ESP-01 is using a two battery setup and I'm always unhappy to replace them with still around 1.2V each).

I'm definitely looking for devices with a very low current, especially in deep sleep, no matter if it's ESP's with few GPIO's, several of them or ESP-32's.

Which ones would / could you recommend?

[obod0002]

anybody with knowledge on battery operated ESP's out there?