Why does the phone shutdown and battery drains super fast on 20% or less capacity when taking pictures?

When the phone is 20%ish or lower battery, after taking pictures the os shuts down. I have observed this behavior on 5 different brands (lg, samsung, lenovo, xiaomi, oneplus), across different android os versions, across different camera apps, even on devices with the battery replaced with a new part. The system takes a picture then shuts down. The battery drains almost visibly upon restart, going from 20 to 15 in a minute or two. I've seen it on official roms, flashed roms, rooted phones etc. Hopefully somebody who's an expert in these things can hit this nail on the head.