The battery has “Pb” written on it, so I assume it’s lead battery.
Lead ain’t that dangerous. Just take it out and dispose of it like you do with normal batteries. Clean your hands afterwards and you’re dandy. As for the clock, the battery contacts, and whatever they were attached to, are likely eaten away, but I can’t say that for certain from this photo. If you’re lucky and they’re mostly intact, some IPA scrubbing and a dip in vinegar, and a bit more scrubbing, should take most of the crust away. That rust though, probably some vinegar, maybe a deoxidating agent (like navy jelly?) could clean it off. Even cleaning all of it doesn’t guarantee that it’ll work any way.
^ I second this comment. Lead is only bad if you eat it or it somehow gets injected into your body. Wear gloves if you’re worried.
Well, it’s not going to explode because it already has…
But if it’s really so old that it’s lead you should be careful. Is it an antique clock where it has value sentimental or other? If not just toss it.
The mechanism is pretty standard, so if you really want to salvage it, you can replace that (and keep the same hands) but definitely mask up and take it outside to clean the corrosion off. If it’s an antique then this has already happened at least once.
