Same problem here. M5Stack team. Please help to fixing this issue.

I've sent it back to shop and they confirmed it's device problem. And they replace with new one. Now no any problem.

M5Stick (Tiny device with OLED) :-)

I assume you mean M5Stick Gray instead of M5Stack Gray, right?

I've tested take M5Stick Gray battery to M5Stack Fire. It's can run perfectly more than 40 seconds.

If on USB power,Its never turn off. But on battery power is like mention above around 40 seconds and it shutdown. (Battery is full charged).

No any module attached. Only 'FactoryTest' arduino example code.

Additional:
I test flash a Flow 1.2.1en firmware and connected to flow website. Around 40 seconds, it's behavior is restart device. Not a shutdown.

It's very wired. My another M5Fire is normal.

Is it normal behavior of M5Stick Gray to turn off automatically after period of time?

I write arduino code to display only 'Hello World'. And let's it start with battery power. It's suppose to run until battery is run-out. But It's keep turn off (around 40 second).

Or this is malfunction unit?