Ok, I have quite a few of the little 3v Lithium coin size batteries off from Mobo and other devices. some were soldered to the boards, others were just clipped into holders. I've just been dumping them into a coffee cup assuming (I know) that they were mostly dead. Most of the pc's I've broke down are old units I've had for a long time. Just out of curiosity today I checked them and about 70% still read 3v or thereabouts. now I'm not sure if I'm risking a thermal event? somewhere on these forms I saw where a small battery did a fair amount of carnage. So... what are the dangers of these things, and what's the proper handling and storage protocol? I'm not talking hundreds, just a couple dozen or so. Thanks RT

In reality you'd be fairly! Safe and are not likely to have an issue. That said I've posted a few photos of the aftermath of what happens when they DO short . Your first short lasts a lifetime as far as care and safety effects.
A micro cell (well under 1 volt) blew a crater into my solid oak work bench and i had a 5.5 volt cell blast me off my feet. So it's definitely a possibility.

Ideally you'd tape both sides of the batteries separatly. I tend to lay out a strip of electrical tape and drop them down on it. About 5-10 per strip. Then a separate strip for the back side.
Button cells can be recycled at most jewelry and electronics shops. Or sold to large steel buyers.

If you are going to keep them loose just make sure it's cool and dry. And do NOT seal them in. coffee cans are best. Heavy sides and base.
Leave the can open and under 1/4 full. That way if they do short and blow the blast is directed in one direction, up. Away from anything else.

OMG I may have to think twice about how I am storing mine, you may not want to know LOL
They are in one big pile inside a heavy steel drawer, I really do need to tape them though.

Ohh! Film it when the drawer shoots out across the room and put it on YouTube.
Lol
In real life most people won't ever see a catastrophic short. Even when they try. But by no means does it /not/ happen. I run into issues because I'm dealing with mostly older pre 90s equipment and original in many cases, at that. 35-40 yo batteries aren't as strong as they once were in terms of shell.

I never worry about my li-ion cells or packs shorting as I am careful with them. I try and tape them as soon as I get them.

Shot across the room was a facetious reply.

What a great in information shared here. Thanks all.