I’m pretty sure the socially unacceptable behavior from homeless drug addicts is driven by factors that drive homelessness and drug addiction and not by the preference of most people to avoid homeless drug addicts in public spaces. Unless you’re implying law enforcement or society at large “clean up” public transportation…
The percentage is based on voltage for lithium batteries. Old or weak batteries will suffer voltage droop when under load, so the device is powering down to protect the battery from over-discharging and causing damage (or a thermal event).