It's pretty easy to run a pi on a battery.

Eh, it's probably OK either way. People have been saying since day 1 that Raspberry Pis are not low-power devices and they're probably right.

Everything is relative, though. In terms of maximums, a Pi 4 (for example) can use up to about 7 Watts under load by itself, which adds up fast when operating on batteries.

But a single 1 meter string of 144 WS2812B LEDs can suck down up to around 43 Watts, and 43 is a lot more than 7. :)

Lighting rigs are thirsty. The processing (even if it's the whole Pi) is generally a small drop in the bucket.