It lasts for days in the lower troposphere but years in the stratosphere. And kg for kg, H2O is a much stronger Greenhouse gas than CO2, so the long-term averag

It lasts for days in the lower troposphere but years in the stratosphere. And kg for kg, H2O is a much stronger Greenhouse gas than CO2, so the long-term averaged effect is on the same order as CO2 (maybe higher, depending on conditions). And sure, I guess you could argue lithium-air is a type of fuel cell (or that hydrogen fuel cells are a kind of inefficient battery), however lithium-air is much more energy dense (volumetrically) than hydrogen-air and both the "fuel" and the "exhaust" are solid and stay in the battery, which has operational advantages. (Although to be completely fair, hydrogen fuel cells are high TRL whereas lithium-air is still lab scale at best.)