If you put a a large group of these atoms together, the escaping electrons from one atom can bump into other radioactive atoms, disrupting them and enabling more electrons to escape. If the number of radioactive atoms bunched together is small, you will get a by-product of heat. If the number is larger, you could have an explosion. From heat, they could make electricity. And because the radioactivity of plutonium lasts for thousands of years, one could have a virtually unlimited potential of power.
Batteries lose their juice and go dead.
Solar panels only recharge these batteries if there is sufficient sunlight. Back in 1959 the AEC clearly recognized the benefit of a perpetual generator for powering electrical equipment in everything from satellites to space probes, and the idea has been popular ever since. RTGs are not nuclear reactors and have no moving parts. They use neither fission, nor fusion processes to produce energy. The heat generated by this natural process is changed into electricity by solid-state thermoelectric converters.