One little point I want to clarify is that if your Apple Watch battery did indeed short and none of the protections against shorts worked, you'd likely just have a burn on your wrist. 309mAH isn't all that much energy assuming a full charge.
I once bridged a ~2,500mAH 18650 battery that was in my bag when my keys created a circuit between the anode and the cathode. The result was a small fire inside my bag that was quickly stamped out. Now, if I'm carrying batteries capable of dumping a lot of current quickly, I use cases.
What excites me most about this new battery tech is home and commercial backup energy storage that's much 'greener' and cheaper than lithium. There is a lot of space in rural and grid settings, so the density of Li-Ion isn't really needed.
Well, shorting out is a fairly realistic scenario, as opposed to a flash-boom, but it is still a relatively slow release.
I was really talking about how much energy potential is stored in batteries. In batteries, the energy is generally stored as potential chemical reactions, so it isn't realistic to have a flash-boom.
Supercapacitors, on the other hand, may have more of a boom potential.
most, and i do mean most 18650s have a circuit board in the endcap that manages the charging and discharging, so a dead short will generally cause that board to heat up and let out smoke. If you did manage to actually short an 18650 (it's not difficult, remove the plastic on the outside and jam a flathead in between the positive cap and the battery body, where the insulator is), it doesn't just "make a small fire, easily stamped out".
if you'd like i can go dig out a 26650 that i have where i dropped it and the board part popped off; but i am sure there are websites with pictures already.
> If it were to all release at once, I'd no longer have a left hand.
Well, super interesting.
At first I doubted because the apple watch has very little energy, then I looked it up. Turns out the biggest ones have 2Wh worth of power. Doesn't seem like much until you consider that 2Wh is roughly 6000J. Bullets are launched in the neighborhood of 1000J.
I wear an Apple Watch. On my wrist, is a small, Lithium-ion battery, that contains a great deal of power.
That power is trickled out, over time.
If it were to all release at once, I'd no longer have a left hand.
Packing all that energy into smaller and smaller form factors, increases the risk; no matter what tech we use.
Energy is energy. When it comes out quickly, we call those "explosions."