user61096: I am building a device using an Arduino Nano, an OLED display and infrared thermometer sensor. I want to make it rechargeable so I am using a 1 cell lipo battery and a tp4056 circuit protection board, which cuts power at 4.2 V and 2.5 V. The OLED runs in the 5.0 V port and the sensor runs in the 3.3 V port in the Arduino. Of course the system does not work since the battery only delivers 3.7 V and when I measure the voltage in the Nano, it is actually seeing around 2.6 volts in each port (I'm assuming this drop is due to internal resistance of the cables and the protection circuit). Having said that I was thinking about using a boost converter but everything I find online says that the input voltage for the boost converter should be at least 3.5 V for it to deliver a constant 5.0 V output. This would not work since as I mentioned, the protection circuit will cut the power at 2.5 V which is well below the 3.5 V mark. Is there another practical solution I could use for this system to work with 1 cell lipo battery. I don't want to use 2 cell battery pack since it would make it more expensive and bigger in size. Also, I ran the project with a 9.0 V battery and it worked perfectly fine.

user614: This is exactly why the typical LiPO battery shield includes a boost converter.
I'm not sure where you saw the unusually high (3.5V) low-voltage limit, but that isn't typical of most converters.

61096: <p>I am building a device using an Arduino Nano, an OLED display and infrared thermometer sensor. I want to make it rechargeable so I am using a 1 cell lipo battery and a tp4056 circuit protection board, which cuts power at 4.2 V and 2.5 V. The OLED runs in the 5.0 V port and the sensor runs in the 3.3 V port in the Arduino. Of course the system does not work since the battery only delivers 3.7 V and when I measure the voltage in the Nano, it is actually seeing around 2.6 volts in each port (I'm assuming this drop is due to internal resistance of the cables and the protection circuit). Having said that I was thinking about using a boost converter but everything I find online says that the input voltage for the boost converter should be at least 3.5 V for it to deliver a constant 5.0 V output. This would not work since as I mentioned, the protection circuit will cut the power at 2.5 V which is well below the 3.5 V mark. Is there another practical solution I could use for this system to work with 1 cell lipo battery. I don't want to use 2 cell battery pack since it would make it more expensive and bigger in size. Also, I ran the project with a 9.0 V battery and it worked perfectly fine.</p>
 614: <p>This is exactly why the typical <a href="https://www.instructables.com/id/Arduino-Battery-Shield/" rel="nofollow noreferrer">LiPO battery shield</a> includes a boost converter.</p>

<p>I'm not sure where you saw the unusually high (3.5V) low-voltage limit, but that isn't typical of most converters.</p>
