The human body could potentially serve as a very good thermal reservoir, as its internal temperature remains quite constant at around 37°C and is stabilized by continual intake of food. Suppose an inventor designed microscopic engines that could be implanted under the skin in order to charge batteries or power other equipment (e.g., pacemakers, or other necessary medical devices) by using the temperature difference between the interior of the body and the outside temperature. If such an engine were capable of half the Carnot efficiency and were able to store 5.0 nJ of energy in a battery in the course of a day, at what rate would the body be supplying energy if the temperature of the surroundings were 20°C?