I have one question though. I know they replaced the fuel cells with batteries because the cryogenic oxygen and hydrogen would have escaped during such long duration missions, but what did they do then for breathing air on the trip up and and, most importantly, back down?
The problem wasn't that the reactants would escape their tanks, but that they couldn't carry enough to operate the fuel cells at minimum power for the entire Skylab stay, and the Apollo SM fuel cells couldn't be shut down and restarted in flight.
So the logical thing to do was to operate the fuel cells until the hydrogen was depleted (which came in handy during the first visit before the one remaining workshop panel was deployed), then shut them down to preserve the remaining oxygen for breathing during the trip home. The CM also had a "surge tank" to store oxygen between SM jettison and splashdown.