They are 5V tolerent on the logic pins, just not on the power. LiFePO4 batteries work great for powering them as their voltage curve matches perfectly without regulation.
My understanding is that this is mostly a dangerous myth. Like it sort of works but you really shouldn’t unless you are ok frying the board. I have been sticking with mostly 3V components and have a separate set of rails and transistors to control that side of things.
No, that's wrong. The signal pins absolutely are 5V tolerant (confirmed by the CEO of Espressif) and work perfectly but if you put 5V to VCC it will fry instantly. I know from experience, in both cases.
It used to be the case that people were unsure if the logic pins were 5V tolerant or not due to ambiguity in the datasheet and the consensus was to be cautious, but it has since been officially confirmed that they are tolerant. Some other devices (e.g. relays, some MOSFET gates) might require a 5V output level to trigger, in which case you will need a level shifter/transistor, but 5V inputs to the pins are fine (and most digital devices that work at 5V logic levels will be fine with 3.3V logical high due to the way TTL levels are defined).
And, the built in A/D will give you the current voltage reading with no additional wiring so you can post it to your MQTT instance and monitor when you need to change/charge your LiPO :-)
