Hmmm, wait a second, I think everyone, including myself has been working with the assumption the mass shifts from the charged battery to the uncharged one, and stays there. That would require that something else shifts back the opposite direction to maintain center of mass and conservation of momentum. But what if it doesn’t stay there? The initial condition we see is unbalanced and so not a stable condition. Once one battery discharges and transfers mass to the other, what is to prevent the other from doing the same thing? In a MGS, the motor and generator are basically the same thing, depending on where the input and output are taken. So here is the scenario I see: The situation starts out with a charged battery and an uncharged battery, separated by the MGS. The charged battery will discharge into the motor and drive the generator, transferring charge to the other battery. The process will not stop when the charges are equalized because angular momentum keeps the rotor spinning past the equilibrium point. Now there is a charged battery on the generator side and a discharged battery on the motor side. So, the roles reverse and the motor and generator swap places. The system is an oscillator, with the charge going back and forth indefinitely. It won’t stop because of friction either because the system is completely isolated; there is nowhere for the heat to go! The instantaneous center of mass shifts back and forth but the average center of mass is conserved, as is the average momentum.