Low battery is probably as close to physical suffering as a robot could experience. Especially if the motors start to draw the voltage very low. That would drive up amperage as the motors start bogged, heating up wires, potentially tripping circuit breakers and probably sending warnings as servos and motor drivers often monitor the currents draw to act as limit switches and safety measures.

Programmers have also essentially tied battery levels to “anxiety” in robots, to ensure they prioritize charging when needed.