Power for Teensy 4.1?


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Handheld Schematic.jpg

The attached image is a schematic of a Retropie hand held I've made.

The blank square you see is just a circuit board I created to make splitting up the power easier.
The audio amp gets it's signal from from the LCD audio out through HDMI.
The Teensy is connected through USB to the 3B+ for power and to run the M8 headless software.

It all works but the problem is the 3B+, the LCD and the Teensy draw way too much power and the battery drains too fast. Battery 1 lasts forever because the LED circuit and the audio amp draw very little power.

So here's my question, if I power the Teensy from battery 1 will it fry the teensy or the 3B+ because of the USB connection? In other words, if the teensy is supplied power will it continue to draw power from USB and/or possibly supply it to the 3B+ causing... issues?

Sorry if this is a dumb question but I only know enough about these things to get myself in trouble LOL I started out following this video: https://www.youtube.com/watch?v=x1RHdH-nlmg but I had to go off road because some of it just wouldn't work for me.

Any help would be really appreciated. And if you need more details please let me know what it might be.
There is a trace on the underside of the Teensy near the pin 0 corner - shown on the Teensy card.

With that safely and properly cut (don't cut too deep) - the Teensy will not take any power from USB ... and won't work without applied external power.

Then from Battery 1 the StepUp to 5V power could be applied to the Teensy VIN pin. With proper power applied there the Teensy will run and also be responsive to the USB connection, without pulling any power from USB.

Not an EE ... connecting the USB cable will tie the GND together between the Teensy and the 3B+. Not sure if that might cause any noise or other changes with two 5V StepUp units in use?