Being much like car batteries, deep cycle marine batteries also contain sulphuric acid.  Although the particular battery with which i had an interaction was of the sealed type that does not require topping-up, I discovered that "sealed" is in this case a relative term.

    This battery was installed in a very small and rather old boat.  Old like classic, not like ratty.  The boat was a late-Sixties two-seater not much larger than a big PWC, with an interesting twin V hull and an overall shape reminiscent of a Corvette of the same era.  Originally, the boat had an orange 15 horsepower outboard motor that, by the time I was using it, was good for little more than burning a lot of oil and constantly breaking the shear pin that transferred power to the propeller.  This becomes a real problem when you run out of spare pins and have to paddle back--there's only room in the boat for a stubby canoe paddle and it's only a fun boat when it has a working motor.

    So we replaced the motor with a shiny new 30 horsepower Mercury. Not only was this new motor at least twice as powerful as the old one and not plagued by shear pin issues, it had an electric key start.  Though ubiquitous now, when the boat was made these were not so common.  Hence the problem: the boat now needed a big, heavy, acid-filled battery it was never designed to contain.  Bearing in mind that with the new motor the boat was quite capable of completely leaving the water should the operator choose to aim it at a wave, someone probably should have thought of a way to secure the battery.  But we were having too much fun jumping waves and generally tearing around.  After one particularly hard landing, I felt something fall against my foot.  "Something" was, of course, the battery.  The overturned battery was now leaking acid in the bottom of the boat and on my boot.  Wisely I chose to made a hasty return to the dock.

    First things first--I return the battery to its upright position.  But now the acid was mixing with the with the bilge water that tends to accumulate in the bottom of boats and covering a much larger area with foul-smelling and corrosive brew.  Luckily for me my boots are made of sturdy leather and protected my feet from harm.  Luckily for the boat, the hull was made of fiberglass, which turns out to be fairly resistant to battery acid.  However, I didn't want to test the limits of this resistance and so I ran to fetch rubber gloves and baking soda to neutralize the spill.  With the seats removed, I started to pour the baking soda on everything that looked like it has acid on it (which is just about everything on or in the bottom inch of the boat).  It was like elementary school science class, all bubbling and fizzing "volcano" in the boat and on my boots.  Exciting!  But it really was everywhere and I had to get on my hands and knees with the box of baking soda and a sponge to reach the affected areas of the hull.

    I managed to clean up the spill.  Neither boat nor boots seemed to have sustained lasting damage, and the battery still worked.  Mission accomplished, right?  But I had forgotten the fact that I was on my knees in the acid swill.  Pretty soon my legs began to itch, burn, and attract my attention.  Lo and behold, many holes have begun to form in my jeans!  The pain and holes both increased apace, and I had no choice but to whip off my pants and bring them with me as I leapt into the lake.  My embarrassment at neglecting to protect more than my hands and feet was compounded by the fact that I habitually go commando.  Needless to say, things could have turned out much worse.  I still have the pants, too.  This was my experience with battery acid.