There were four basic materials that the Egyptians used to build the pyramids: limestone, pink granite, basalt, and alabaster. Each type of material had a diverse use. Limestone had, for the most part, two uses.
To answer your question: The useful lifespan of a CPU is about 3-4 years. My guess on the technical lifespan under full load is closer to 8-10 years if nothing else breaks and takes the CPU with it. The reasons: High Performance Computing Clusters usually keep the computers for 3-4 years.
Some might last a year or two, others a decade. Some BIOS will lose only the time, others will lose more. Some machines are designed to make it easy to replace the battery, others not so much. My advice: donât worry about it until your PC starts losing the current time and date on every boot up.