found this
"Interplanetary satellites that fly toward planets such as Jupiter and Saturn are so far away from the sun that they cannot use solar panels to generate electricity. These satellites use RTGs (radioisotope thermoelectric generators) to generate their power. An RTG uses radioactive material (like plutonium) to generate heat, and thermocouples convert the heat to electricity. RTGs have no moving parts, so they are reliable, and the radioactive material generates heat for many years."
but you need radioactive materials, maybe it can work in a small amount without being unsafe
there is a way to convert the heat from device that use electricity, to electricity again? i think it may be against the thermodynamic law
The GPHS-RTG model used in most recent missions uses 7.8kg of Pu-238 and generates 300W of electricity. If you can find 35lbs of plutonium, you could power an S5 this way using two of them. Of course, rather than using them to power an S5 you might want to sell them to NASA for $50M each.
You can recover heat from a device using the same effect, but you need a temperature differential across your recovery device. Essentially, you do so at the cost of making the miner run hotter all else being equal.