I was listening to the Plutonium episode of "the Elements" on the BBC, and between 07:00 and 08:30 they talked about uses of plutonium such as spacecraft power and heat. While the returning astronauts in Apollo 13 were not actually "keeping warm" using the RTG, I didn't realize that the spacecraft actually had RTGs.
In this answer I found that indeed the Apollo 13 LEM contained an RTG.
Was it just the one RTG per LEM that was used in Apollo spacecraft, or were there more? Were they just used as a passive, steady source of heat to insure things didn't get too cold, or for a source of power also?