Witty Pi L3V7 - Pi Zero 2 - Waveshare SIM7600G-H Won't Start on Battery

Hello all,

I have the following assembly that I want to be powering from a battery I am recharging via a solar charge controller (see image).

• Witty Pi L3V7 (capacitor between the 3v3 and GND pins)
• Pi Zero 2
• Waveshare SIM7600G-H

The assembly is stacked as in the picture.

While when I'm powering the assembly via a USB connected in a wall plug it powers up correctly, when I'm trying to power it from the battery charge controller (both USB and 12V to 5V/5A step down converter) it doesn't want to start up.

Any one has an idea on how to resolve this issue?