I have the same problem the same message
I have several 5000Mh 3S batteries, the low voltage message happens when the battery drops the charge level to 11.60 volts.
When the battery is charged it shows 13 volts and the raspberry works fine until the voltage drops to an average of 11.70 volts.
Did I get correctly that you use Raspberry Pi 4 as well?
YES, only raspberry pi 4
Is there any chance you can try to power your Raspberry without the power module and check if it works?
With the multimeter I am monitoring the voltage of the batteries and the voltage of the power module of the navio2 raspberry pi 4.
there is a difference of 12 volts less in the power module with respect to the battery.
If the battery reads 11.80 volts the power module reads 11.68 volts.
The raspberry pi works perfect as long as the voltage on the power module reads 11.70 volts or higher.
I have two 5 volt 3 amp cell phone chargers. One brand sonny and the other brand sansung.
In both I get the same problem with the low voltage message.
I have a voltage adapter for raspberry pi 4 brand VILROS and with this it does not give any error message for low voltage
Thanks for sharing these details. It’s good to know. I need a bit more time to check it myself, and I’ll get back to you.