Final answer:
Smartwatches and wall clocks are the devices that typically use batteries as their main power source. Desktop computers and microwave ovens rely on outlet electricity and have much higher power requirements.
Step-by-step explanation:
The devices that make use of a battery as its main power source from the given options are: B) Smartwatch and D) Wall clock. A smartwatch is typically powered by a rechargeable lithium-ion battery, while many wall clocks operate on a small alkaline battery or a button battery, like the one depicted in Figure 5.5.1.
Other options such as A) Desktop computer and C) Microwave oven primarily use electricity from an outlet as their power source and are not designed to run on batteries. Desktop computers require a stable and continuous source of power that batteries cannot efficiently provide for extended periods. Similarly, microwave ovens consume a lot of energy when running, which would quickly deplete conventional batteries.