Hunger:
    The robot will feel hunger as its batteries get low. The lower the batteries, the greater the hunger for a recharge (or a swapping of batteries). (While its batteries are unplugged, could carry it on a backup battery which is recharged by the fresh batteries after they are plugged in.) The robot will not have to respond to its hunger instantly, and this will be one of the nagging feelings which the ego will balance against other priorities. If the robot is in the middle of something important or something it wants to finish, it may choose to put up with the discomfort of energy hunger until it has finished what it is doing.