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Quick and dirty guide to Lithium battery-powered Wemos D1 Mini

The Wemos D1 Mini is an ESP8266 based prototyping board with WiFi connectivity and countless applications. It becomes even more useful in battery-powered applications, where with the proper setup, it can run low-powered for months at a time — or only hours if done incorrectly.

This is the quick and dirty guide to running a Wemos D1 Mini powered by Lithium-Ion batteries: We will be blatantly ignoring several design specifications, so double check everything before using in a critical project. Several things will vary, and since there is plenty of clones of the board some boards will work better than others.

Warning: Lithium-Ion batteries always command healthy respect, due to the energy they store! Do not use bad cells, and do not leave batteries unattended in places where a fire can develop, especially while charging. That being said, the setup given here should be as safe as most other Lithium-Ion battery projects.

Why run off a battery?
You chose a Wemos D1 because you want to do some WiFi connectivity. This narrows down the useful modes from the overwhelming large table of possibilities. The approach will be slightly different depending on why you want to run off a battery. There are 3 main usecases:

- Periodically wake up on a timer, do some work, connect to WiFi, and go back to sleep. Here we can utilize the deep sleep mode of the ESP8266, and get lifetimes in months.
- Wake up based on an external pin trigger, do some work, connect to WiFi, and go back to sleep. Here we can also utilize deep sleep, and get lifetimes in weeks/months.
- React with low latency to an external pin, do some work, and go to sleep while still connected to WiFi. Here we can utilize light sleep, but only get lifetimes in hours/days.”

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