Ok, I see you want to poll the data instead of push.

Blockly, which is great for simple projects or quick test of a sensor, seems to lack of many functions. It is also not very comfortable for extensive projects and you are required to use a cloud service to edit your code or you have to use a very old desktop version with even less functions. My oppinion about that.

I prefer the Arduino environment. There are many libraries and examples including web servers.
It means a bit more of text coding and less drag&drop but copy&paste from examples work for me well.

EZData is just one of the possible data storages. With M5 products it is very easy to use. It is also possibe to use other cloud services. Cloud means "some storage somewhere on the internet". It requires a connection to the internet anyway.

Some ideas:

• Use a separate non interupted connection such as LoRa or mobile internet for your battery measurement. Depends on what is possible at your location and what/how you need to communicate.
• log to a cloud like storage in the local network, powered by battery on mains loss. No access during power loss but all data saved
• Detect the internet connection loss and log to SD card until the connection is back, then upload all missing.

Prüfe die serielle Verbindung zwischen dem StickV und dem Gray. Möglicherweise stimmt da die Verdrahtung nicht (Rx/Tx vertauscht).
Falls das nicht hilft, würde ich am StickV eine Debug-Zeile einfügen die auf dem Bildschirm ausgibt was über die serielle Schnittstelle ankommt (es soll ein "/" sein). Am besten gleich unterhalb von Zeile 35 (if data[2] == "/" :).

Check the WiFi frequency band. ESP32 is only compatible to 2.4GHz WiFi networks. Some iPhone use 5GHz by default but there is a compatibility mode for switching down to 2.4GHz.