[_hypx]

The other issue is that metal-air batteries go by another name: fuel cells. You are power-gated by how much oxygen you can deliver to the battery. As a result, metal-air batteries/fuel cells are either very slow to discharge, or have big air pumps to have decent performance.

And of course, they will release oxygen if you try to charge them, which implies a way of rapidly expelling air when charging up quickly. Many past attempts avoid this problem by "mechanically" charge up the battery, meaning literally swapping out the spent chemicals with new ones. This of course require an auxiliary battery if you want regenerative braking or the ability to electrically charge.

And of course, the real catch is that we've already invented the metal-air battery in a practical way: hydrogen fuel cells. The big advantage with them is that mechanically recharging is very straightforward compared to other mechanisms. All other attempts are basically reinventing the wheel or have a very specific niche in mind.

[pfdietz]

A problem with fuel cells is that if they're acid, they need expensive platinum group element electrodes. If they're alkaline, they can use nickel, but then they need to have the CO2 scrubbed from the air or they clog up with carbonate.

[frankus]

But there's something to be said for a fuel that's solid under ambient conditions rather than being literally the least-dense substance on Earth.

[_hypx]

Methanol fuel cells exist too.