Using External Power and USB with the Teensy USB development board
Enable your Teensy with a Colorful LED Display Shield
Arduino (Teensy 3.2) Power Issue - ESK8 Electronics - Electric Skateboard Builders Forum | Learn How to Build your own E-board
PJRC (Teensy) Forum
Teensy 3.x Feather Adapter : ID 3200 : $5.95 : Adafruit Industries, Unique & fun DIY electronics and kits
arduino - Strange problem with Teensy 4.0 connected to external power only running code when serial connection is introduced - Electrical Engineering Stack Exchange