Some batteries, especially if overheated due to getting shorted out, can produce hydrofluoric acid. See section 10 of this from an example at Duracell’s web site on one of their battery types.
So, if you have a battery overheat, burn, explode, etc. Get thee to an ER.
I worked in a petrochemical plant for many years, on the other side of the fence (about 200 ft) was an “Alkilation unit” for a gasoline refinery. HF acid was used in the Alki unit. It is a one of the strongest acids and very dangerous. I understand a small exposure on the skin will attack the nearest bone if not neutralized. Over the years they had some people exposed to the HF acid but there was no loss of life. They used the stuff by the tank car loads. I think we had about as many people burned with caustic in our caustic treating unit than they did in their Alki unit.
Along those same lines, hydrochloric acid is an exceedingly strong acid, the strongest of all the commonly-known acids (and possibly the strongest known, but I’m not sure of that). But it’s not particularly dangerous. If you spill concentrated HCl on yourself and walk over to the sink to run water over it, you won’t suffer any noticeabe injury. In fact, it’s the acid produced in your stomach, in the normal course of digestion.
Undergrad usage? Heck, in the mid-60s my high school chem class used it to etch glass. I don’t remember any injuries or special precautions. Of course, at that time mercury wasn’t considered a particularly hazardous material, either.
Back when I worked at a paper & chemical distribution warehouse, we sold a product that contained hydroflouric acid. It was made specifically for removing rust, but somebody figured out it could be used for another purpose not related to rust removal.
When people asked if it could be used for that purpose, I would always tell them no. Other employees would tell them yes. I warned them that the company faced potential lawsuits for doing this. Of course, they didn’t listen. Luckily, it never came to that.
We did have a customer who was given a sample of a similar product by a traveling chemical salesman. She used the product in the way it was not meant to be used.
She got the stuff all over her fingers. Within a few hours her fingers began to burn and itch. Eventually, she lost the tips of six fingers.
She successfully sued the chemical company because of this.