Atomic battery
An atomic battery is any device that converts Radioactive Decay into electricity. They are typically simpler than fission or fusion reactors, and require less maintenance and monitoring.
Importance to Martian Settlement
Atomic batteries offer a short term solution to power generation needs. They show the most promise for initial settlements and outposts. Their high power to mass ratio makes them ideal for shipment with the initial settlement materials, where they can provide power while other generation methods are developed. Unless significant deposits of radioactive material are discovered on Mars, the only way to build them is to import the material from Earth. Alright alright alright that's eaxtcly what I needed!