system
Given the following post, respond as if you're commenting on Reddit:
human
Do discharged batteries weigh less than fully charged batteries?

All things being equal other than charge. Do expended batteries weigh less than full? 

Hypothesis: I'd say yes, as chemical energy is being converted to electrical energy and then sent out of the battery there must be some loss of mass. 

-edit-
Thanks everyone! As with most scientific things, this has only lead to more questions;)
gpt
Answers depend on the specific battery chemistry. Zinc hearing aid batteries will gain mass for example. An A675 will gain about 200ug as it discharges from the oxygen and CO2 it captures from the atmosphere.

Lithium-ion and NiMH generally lose mass when charged due to the parastic gasses produced (mostly hydrogen and oxygen) they'll sometimes incorporate little pressure valves in their design to vent these volitiles.