When working with our current iterations of maker BCI [Tee-naps _v0.1, Pi-Naps_v0.2] it's likely that you wont have much luck running the device using USB power.
Unfortunately, USB power on these devices is very noisy and you may find that this heavily detriments the EEG signal you are measuring.
These devices are designed to be used with a battery plugged directly into our board using the commonly used 2-pin JST-PH connector.
This also may extend to the use of HDMI on the Raspberry Pi. These are limitations we will be continuing to explore solutions for.
PLEASE NOTE : To use Teensy 3.2 with Tee-Naps, you will need to cut the VIN -> VUSB connection on the PCB (as described in the Teensy documentation) for use with an external charger.