My issue is not with gas nor even the acid. It is with long term effects of fooling around with batteries without using gloves, and playing with charging batteries (bubbling vigorously) without wearing a mask. Get a white cloth, rub it on a battery or near a battery. See the almost black smudge? That's lead sulfate not pure lead. No it doesn't put you in the hospital right away. But later on in life when a sudden autoimmune attack, heart rhythm problem, kidney or liver issue suddenly appears you can bet lead had a lot to do with it. I wasn't referring to batteries in outside compartments, rather flooded batteries being stuck under sinks or in closets and cupboards without benefit of proper ventilation.
Do yourself a favor and GOOGLE the term LEAD POISONING.
When inverters manage to acquire skin and lungs then I'll include them in the list of warnings.