[spijdar]

I can't tell if this is satire or not, but taken in good faith, how?

A fully charged battery would necessarily have more mass than a fully depleted battery, but the difference should be so tiny as to be immeasurable. Or am I wrong? We're essentially talking about the sum weight of a bunch of electrons, which are extremely light. There's no other exchange of matter going on when charging/discharging a battery, just the creation/destruction of chemical bonds, and associated movement of electrons.

[btilly]

A battery doesn't have a static charge. When it discharges, electrons move from one side to the other, then back through the batter, and you modify which atoms have which elections. But it continues to have no static charge.

However it has less potential energy. And therefore you change mass by the mass associated with that potential energy.