*Even captured alien ships, if anyone has one, and a budget, I'm game to help.
I saw a Nissan Leaf get a battery back replacement at the dealer. The adjacent bays were closed off as well. When asked the reply was something about the high voltage has killed 1-2 techs and now Nissan mandates they close of the bays during a battery pack swap.
12V is Extra-low voltage. High voltage is > 1000V (with specific risks due to electric arcing).
With 12V you can't get an electric shock, and the biggest risk is short-circuit (which is where you can get cauterizing metal pieces) and then the battery itself is the most sensible part (Lithium battery really don't like short-circuits): battery fire is a much bigger hazard than burns.
Also, the short-circuit risk already exists with lead battery (even if the amperage is lower).
Any well-designed battery pack should have some kind of integrated short-circuit and temperature protection, though.
The specific hazard discussed above was about overheating a wedding ring or a watch. With 100 A, you'll reach that point in around 100ms. No need for long time at all, and a lead battery poses the exact same risk in that regard.
Using the equation V (volts) * I (Amps) = P (watts) we could calculate the power of putting a car battery through a ring: 12 volts * 100 amps[1] = 1200 watts. That's more than your average microwave.
The reason you don't heat up when you touch a car battery is that at 12 volts your skin (mostly an insulator) won't conduct the needed amps. Metal (a conductor) will however transfer close to the full 100 amps of the battery.
Here's an example of the effect[2]
[1]: https://www.bestpowerbattery.com/how-many-amps-is-a-car-batt...
It's generally immediately obvious, and can be remediated by pulling the cable away before it welds. But dropping a screwdriver in the wrong place can and will (statistically, thanks murphy) happen, so better use insulated screwdrivers and gloves, to reduce the likeliness of it happening.
The current won't flow through your hand, 12V is too low to pass your skin with a significant current. The only way the ring can have raise to a significant heat is if the ring itself touches both sides of the circuit (anode -> car frame -> ring -> wire -> cathode). Anode -> car frame -> hand -> ring -> wire -> cathode won't cause any short, because your hand acts as a big resistance in that circuit.
Of course not, I didn't mean to imply that.
> if the ring itself touches [the car frame]
That's what I meant.
> 12V is too low to pass your skin with a significant current
Now of course the human body has a complex impedance, with cell membranes acting as capacitors: higher frequencies let more current flow. And that also depends on how much skin there is (single finger vs arm to foot), if it is wet, etc. I remember trying a (discharged) 9 V battery on my tongue as a kid... that was literally quite a shock, even with continuous current.
In the end, I wouldn't bet that an electrocution is impossible using a mere 12V of electric potential.
Anyway, given that 12V is considered safety voltage for submerged swimming pool material in France, I'm pretty confident it is be extremely unlikely to kill anyone.
A 12V car battery can supply hundreds of amps if you give it a low enough resistance to go through.
As for the heating up... https://www.youtube.com/watch?v=nbGcSjRAyxs is a good demo of how fast 12V can heat up a small hunk of metal given enough amperage (in the case of that video 12V at 100A) . There are a surprising amount of 12V and 24V DC power systems (like in that video) can push in well over a kilowatt (12V at >100A or 24V at >50A) of power in a dead short situation.
My father had a paperweight in his shed that looked like someone used a spanner as a fork for lava, drooped away from its normal shape like a Salvador Dali clock, one end barely recognisable with blackened carbonisation marks and a ragged but lightly polished place where it was cut clean from something with an angle grinder. 24V at 150A for just a few seconds before the batteries were discharged, big marine batteries for lots of current to kick start an old heavy duty engine, lots of Amps but not many Amp Hours, still enough to destroy the spanner.