Recommended max number of physical LED's

Using a typical 5V USB without high-current capabilities, it should be safe to power

• 10-15 NeoPixels at moderate usage (around 20-30 mA per LED) = 300-450 mA
• 5-8 NeoPixels at full brightness (60mA per LED) = around 450 mA

...accounting for an extra 100 or so mA for controller, and remembering standard USB 2.0 ports are typically rated for 500mA, and USB 3.0 ports 900 mA

USB-C (depending on source) can supply 500mA to 3A at 5V (ignoring negotiated higher power levels), meaning you can power more!

• 50-75 at moderate usage = around 1.8-2A
• 25-30 at full brightness = around 1.8-2A

If using a 18650 battery, we can indeed power around...

• 50-75 at moderate usage
• 25-30 at full brightness

Battery would probably be drained in 1-2 hours.

If using a boost converter, that might also start to get a bit hot!

So huge amounts of LEDs sound great, but logistically you might want to be somewhat wary.

USB power rather than battery will of course remove the problem of battery life.

Power observations

Personal experience - test rig with 64 rgb pixels had zero problem off a bog standard USB socket.

Normal ticking over of test device with no LED's was around 0.6 watts.

Having 8x8 LED test board plugged in ate an extra ~0.04 watts/~20mA of power without LED's being lit.

6 LED's coloured outputs full brightness device total hits about 1.15 watts

OLED screen measured around ~0.02 watts power/~10mA (device specs specify max ~0.08w)

18650 using 1watt of power theoretically might go for about 10 hours in ideal conditions.