Batteries blow up, fires are caused, machines are damaged, and people are seriously hurt around batteries. Your caution is appropriate.
Invest in a meter, wear safety equipment like glasses or a face shield, think. When in doubt, don't! If a few bucks is the problem, take a second job.
Lead-acid cells are dangerous for many reasons-- hydrogen gas is given off, acid eats through skin and clothing, explosions happen. That's not to say that other batteries (GEL, AGM, etc) are safer, they are not.
A friend decided to add another battery to his RV. He placed it aside the first one, but in the dimly lit and fined space, he proceeded to connect the interconnecting wiring. Upon contacting the terminal with his last wire, the battery exploded.
His face was burned by the flash, acid ate his shirt, the wire he used was vaporized in the middle, the new battery was ruined. Heís lucky, he isnít blind, or worse-- dead. Fortunately, he wears standard glasses, but, he wasnít using safety glasses or a face shield which is why his face is like it is.
Obviously, no one really cares about the fire caused by the flash which damaged the surrounding area, the battery which is now useless, or the paint-free area cleaned by acid. Who cares about his shirt, too? All of this can be replaced. But, imagine what could have been against what actually was.
Itís your choice.