Leaving a microwave oven unplugged for long periods of time does not have any significant effects or require periodic "refreshing" like batteries. Unlike batteries, microwave ovens do not have a built-in power source that depletes over time.
When a microwave oven is unplugged, it essentially remains in a dormant state. It does not consume any power or generate any internal activity. As long as the oven is stored in a dry and clean environment, there should be no negative consequences from leaving it unplugged.
However, if a microwave oven is stored for an extremely long time, there is a possibility that some of its components may deteriorate over the years due to natural aging or exposure to environmental factors. But this degradation would occur regardless of whether the microwave oven is plugged in or not. In such cases, it is generally more related to the overall lifespan of the appliance rather than the duration of being unplugged.
In summary, there is no need to periodically refresh or plug in a microwave oven that has been left unplugged for long periods of time. When you decide to use it again, ensure that it is clean, in good condition, and follow the manufacturer's instructions for safe operation.