Blynk is not great for projects there long battery life on small batteries is desired.
Blynk requires that the Arduino remains active and communicating with the Blynk servers at all times, in case the user wishes to connect and read the sensors. This drastically reduces battery life.
A better approach is to have the Arduino remain in deep sleep mode for most of the time, only waking regularly for a very short time so that it can read the sensors, transmit the readings to a server, then go back into deep sleep. When the user wants to check the readings, they connect to the server, not the Arduino.
To support this approach, there is a wide choice of cloud-based services, including Arduino's own service, a service from Adafruit, and many others.
Personally, I built my own service, for personal learning. It's not as fancy as the others, but it's been working well for many years now.