So today my car battery died, couldn't even be revived with a jump. I was able to walk to an auto store to get tools and a new battery (damn that mfer was heavier than I expected). I had never had to replace my own car battery before.
I screwed the fastener nuts the wrong way for like 5 minutes, cut my hand, and ultimately accidentally crossed the positive and negative terminals with a wrench that exploded in sparks. I don't even know what stopped me from being electrocuted but I didn't feel a thing.
While I'm happy I was able to take care of it myself and will be able to in the future, I also feel like such a dunce for not knowing wtf I was doing and almost shocking myself
You didn't feel anything because it's only 12V. Be happy it wasn't worse and learn from it!
Yep! There's a lot of confusion in the public sphere about how electricity works, but you cannot electrocute yourself with a car battery alone - you can touch both contacts at once with your hands and you'll feel a tiny sensation at worst.
A common myth is "It's not the voltage that's dangerous, it's the current!" and this is the perfect example of why it's way more complex. Car batteries can deliver lots of current (>40 amps), they have to to run the starter. But at 12v, the resistance of a whole human body means the voltage simply isn't enough to be dangerous under practically any circumstances (other than maybe pushing the battery against your completely bare chest, for a long time, over your heart, also you're soaking wet for some reason).
The only danger OP had was if they left the wrench bridging the contacts long enough, then it would have heated up and melted stuff. Bridging the contacts for a fraction of a second and making sparks isn't actually anywhere near as dangerous as it sounds.
Do some fun experiments with your toes