I am powering my Pi from 2.4.GND gpios. The Pi only shows RED constantly ON led and does not boot. However, if I connect the USB power source it boots up. The power supply designed is strict 5V and max 3A.

Furthermore, once the Pi is all booted up and the USB is removed it keeps working fine and even reboots perfectly. Only when I remove the battery and connect again it does not turn on as if it was shut down.