I have a Pi Dog kit connected to a Pi3. I started construction/connection a few months ago and “life” intervened so I’ve just returned to it. I’m powering it with a genuine Pi3 PSU (plus a Micro-USB to USB-C converter).
I can’t get the Pi to boot with the HAT powered from its USB-C connector: with all the servos etc connected: there is no display on the monitor (connected by HDMI). The Pi boots fine if powered from its own Micro-USB connector.
After disconnecting everything from the HAT and then gradually reconnecting leads, I’ve narrowed it down to the blue rechargable battery. If that is connected (either with no other leads connected to HAT or with all of them connected) the Pi fails to boot or else boots as far as the rainbow square before black screen and mouse cursor, and then restarts.
If the battery is disconnected, even with all other servo etc leads connected to the HAT, the Pi boots fine.
It is likely that the battery, which had been charged originally, has become discharged in the meantime. But would a flat battery, with a Pi 3 PSU connected to the HAT, cause the boot sequence to fail?
By connecting a mains power monitor between the PSU and the mains supply, I can see that the PSU uses about 5 W without the battery connected and when booted. With the battery connected, mains power usage is 10 W even with the HAT’s power switch turned off (so probably just charging th battery). If the battery is connected ot the HAT, the “charge” LED near the USB-C socket comes on when power is applied (and with the HAT power switch turned off). If the battery is not connected, the charge LED flashes. This may be normal - indicating either that the battery is charging or else that there is no battery to charge.
Is it a matter of waiting several hours for the battery to charge, or is it more serious that that - is the battery broken?