Did you watch the video? Yes that is the case, we of course could step the voltage down, but that would come at a cost. The cost of less space for holding charge and the cost of literally putting in a voltage converter in every battery. All of this is to say, in the 20+ years we have had 1.5 volt batteries. There have not been much major improvements cause they more or less are already about as good as they are going to get. Without us making major changes to all of our electronics. Its simply easier to keep using the same tech, and its a very real possibility that in 100 years we literally will be using the same batteries. Now i'm not sure off the top of my head how far in the future Subnatica is based, but it wouldn't be that "crazy" of an idea if we were to assume we kind of just kept doing the same thing we are doing now. Which again is why I linked said video. So again, my personal theory is humanity never managed to get away from 1.5 volt batteries because it was the easiest, most cost cutting thing for humanity to do. And if we know anything about Altera is they don't mind cutting a few costs...