I have mobile setups with PI4Bs and L3V7 with v7 firmware and 1000 mAh batteries. The PI powers an LTE modem and a GNSS receiver. Typical current draw is below 1A, a bit higher during startup. The WittyPi is only intended to allow graceful shutdown when external power is cut and battery Voltage drops below an arbitrary and reasonable threshold.
While I have seen it powering down as intended a few times, most often it does not do that. It is difficult to debug though. I believe pin 4 is not going down and that the witty just cuts power and the whole thing dies. Reapplication of external power works well and powers as intended. Most of the times the PI is powered to somewhere about the threshold, but it sometimes happens that it cuts right after USB power is disconnected and the battery shows to be fully charged after power cycle.
Does anyone has similar experiences?
Thanks.
Your use case assumes the battery provides enough voltage for the Raspberry Pi to shut down gracefully; however, this assumption may not be true in reality.
Actually, a 1000 mAh battery seems too small for this application; the battery voltage will likely drop too quickly, preventing a graceful shutdown.
You could try setting the low voltage threshold to a higher value (e.g., 4V). If the issue persists, you should consider using a larger battery.
@admin thank you for the advice. The cell should sustain 2C current. The input Voltage measured by the witty stays well within the threshold in most cases when the external supply is cut. But somewhere along the discharge of the battery after power cut, typically around 20 minutes, the witty ungracefully cuts power. to the PI. I am inclined not to blame this on the battery capacity, rather that the MCU shuts down or resets (apparently it is functional since reapplication of power is working as intended) I will however try to go up in threshold and see if this makes a difference.