[mkr-hn]

Batteries are heavier when fully charged. Takeoff weight matters. It's not much heavier, but it might be enough to affect things at this scale.

edit: remember the context. This is about an abstract optimization to find the minimum viable aircraft.

[luma]

I can't tell if you're being serious. You are technically correct, but also incredibly wrong in suggesting that the increased weight would be substantial enough to impact anything measurable. Depending on the size and capacity of the cell, you might see a difference due to general relativity on the order of nanograms.

see: https://physics.stackexchange.com/questions/34421/does-the-m...

[p1mrx]

A nanogram saved is a nanogram earned.

[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.

[rrss]

what kind of batteries are meaningfully heavier when charged? are you just talking about like E/c^2?

[jermaustin1]

A water/gravity battery comes to mind. Definitely not the answer you are looking for, but an answer none the less.

[enchiridion]

Depends on your definitions. Is the water pumped considered part of the battery before it’s elevated?

[jermaustin1]

The pumping of the water would be "charging" the barrel of water, I guess.

[einpoklum]

I'm sure this will work great for powering an aircraft, too. You could just let it all hang from an anchor at the highest point in the battery :-P

[luma]

Gas tanks :D