I mean, I could absolutely imagine someone doing this. They're probably a well meaning person, but probably not of great intelligence. They're driving through the desert one day, absolutely thirsty. They're desperate for a drink, about to pass out. Then they remember in their delerium - "Wait! There's some water in the car's battery! I could drink some of that and be fine! I'll just drain it while the car is running (so I don't have to restart it), keep the engine running, and be able to make it to the next town. My God, I'm a genius. I'm saved!" They then proceed, in the manner of unique creativity only the ignorant possess, to find a way to drain the fluid from the battery of a running car engine. And they have a big old swig of that battery water.

What would be required for this? All that it would take is for someone to just have very poor chemistry knowledge. Someone sees a fluid that looks like water, and they assume it's water. Maybe they figure a car battery works like a potato battery and there's just water in the cell. Even if the "water" is clearly foul, maybe someone would assume it's just dirty water, but still water. (As in, not an acid.)

Or, maybe they even know it's not something you should regularly drink. They know there's some fluid called "battery acid" in the battery. But they also know that soda is acidic, and that is safe to drink. So maybe battery acid is OK in small amounts? Just how strong does an acid have to be before you can't safely drink it? Maybe they could just try a small quantity, maybe about a spoonful? Surely that would be fine....

Those on the bottom 10% of the IQ distribution don't deserve to die. Those who failed high school chem don't deserve to drink battery acid.

When planning public health or public safety interventions, you have to balance between cost and effectiveness. For example, imagine some new car widget that will increase automobile safety. You're a regulator trying to decide whether to mandate them on all new vehicles. You run the numbers; you want to balance the increased vehicle price against the projected lives saved. You run the numbers and find that this will cost $1 billion per life saved. Probably not worth mandating them. It's not that those lives aren't worth saving, but there are more cost effective ways to save lives. We could tax everyone the same money they would spend buying these devices, and then use this money to expand Medicare eligibility. Or we could mandate some other vehicle safety device. The number of lives saved is always balanced against the cost of an intervention. The value of a life is infinite; the number of dollars available to save lives is finite.

But printing on a battery? The manufacturers already print a labels on them. It costs tiny fractions of a penny per battery to add the safety warnings. Even if it only prevents a handful of deaths or serious injuries over a decade, the cost is so low we might as well do it. There's something like 14 million new vehicles sold in the US each year. Imagine over ten years that's 140 million vehicles. Let's say it costs a penny to include a warning label on each battery. That's a cost of $1.4 million over an entire decade.

I would say in that case, if even a single life is spared over that decade, if only a single living person is saved from the reaper...Then it is worth it. Hell, that's probably even a fair amount to prevent a life-altering injury. If even one person per decade is stupid enough to drink battery acid, and this warning will prevent it, then it is worth doing!