Strange behaviour Raspberry Pi 4
There are two 5V. TP 1-3 is the input 5V from the mini-usb power connector. The other 5V (the usb 2.0 /3.0 port power) is hardware controlled by the regulator and turns it on after it sends a power good logic to the cpu and receives a clock signal from the cpu. Pins 2&amp;4 should be less than 1 ohm (continuity) between pins them and tp1, tp2, and tp3 located on the bottom side of the board. If your battery is not above 4.63V it will not power up. Usually people will use a low drop out regulator in this circuit. That might be the issue. The only other thing that would be different from powering this from a battery is the usb current sense circuit, that goes back to pin 21 on the circuit. I don't know the logic behind them using that pin, as I seen it grounded most of the time in the tablets that use the MXL7704 regulator. But it shouldn't stop it from running. Low battery voltage will. On the side note, I still don't understand why they didn't put a power switch in circuit, since it is only 5 resistors and a pin header to make that circuit. Here is the schematics they provided (partial). https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_4b_4p0_reduced.pdf