I have an old phone (nexus 5) that I want to use for a project. I need to replace the battery with a permanent power supply, I've found the 3 pins of the battery and made a breakout connection with 1/10" headers instead of the stock battery connector. The phone will boot fine with a battery connected this way. The phone runs at 4.2v, ~500±100mA.
The issue is the phone won't boot on my bench PSU. Recovery mode works but Android powers off midway through boot. I suspected it was the lack of a thermistor in the third battery pin that made it shut down. I measured the resistance and added a fitting resistor between the battery monitor pin and ground (56k). However, the phone wont boot either.
I also suspected a power spike that my power supply could not handle could be the culprit. But after adding a 4700μF cap the issue persists.
I have anoter nexus 5 motherboard that behaves just the same.
What else can be causing the phone to act differently with the power supply and the battery?
Ps: I have access to te UART port of the phone, the kernel does not print anything relevant and the phone shuts down at random boot events, sometimes glitching the line, so I think this is hardware or at least isolated from the main processor.