There are many weird and wonderful humanoid robots out there, but one of the most eye-catching machines launched this year can change its own battery pack — making it capable of running autonomously for 24 hours a day, seven days a week. The Walker S2 robot, made by the Chinese company UBTECH, is 5 foot 3 inches (162 centimeters) tall and weighs 95 pounds (43 kilograms) — making it the size and weight of a small adult. Using a 48-volt lithium battery in a dual-battery system, the robot can walk for two hours or stand for four hours before its...