In this video we make a Tritium Nuclear Battery. This is also known as a Radioisotope Photovoltaic Generator.
This is not like the more common Radioisotope Thermoelectric Generators used on spacecraft as this does not use thermoelectric elements for the energy conversion portion.
The key component is luminous tritium vials. You can find them on online shopping networks as "Tritium Vials" or "Tritium lights".
These lights are simply attached to an amorphous solar cell to produce electricity. More efficient monocrystalline solar cells cannot be used as they are ironically less efficient at the low light levels the vials produces.
The device in the video using 14 tritium vials of 22.5mm x 3mm in size produced 1.23 microwatts at the maximum powerpoint of 1.6 volts.
Check out the video for further details.