From an answer to Astronomy SE question How does Titan maintain the atmosphere
And we know the idea of generating electricity with a coil orbiting through a planet's magnetic field is sound in principle, if you've any doubts see answers to the Physics SE question Can the Earth's magnetic field be used to generate electricity?.
Put together this suggests a potential solid state source of electricity that doesn't require any fuel that will last indefinitely.
For a probe on Titan's surface (perhaps one monitoring atmospheric density & composition) as little as one hour of full power & radio contact with Earth once a week or so may be adequate especially for a backup power system.
So I was just wondering if it has either been proposed, used or tested by any Titan missions to date.