KM: When the oxygen was rapidly depleting, that meant two things to the CSM. First, it was going to lose electrical power. When you run out of oxygen your fuel cells quit, as does your life support and pressurization. The CSM also has two small batteries, but you need them to run the Command Module from the time you separate from the Service Module until you get down on the ground. So we were very, very concerned about doing anything that would tap into the batteries. We said, "Okay, we're gonna stuff these kids in the Lunar Module and live off the LM." The LM has all batteries, no fuel cells.