I have a lead acid battery that requires periodic refill with distilled
water. The caps on the cells are somewhat tight and have very sharp edges and
painful to unscrew with bare fingers. Here is what I came up with so far:
And here is one of them in its natural habitat:
Originally I wanted to have them about 9 mm thick (height of a cap) but just for testing set thickness to 10 layers (≈3 mm). It worked perfect at that size, both strength- and handling- wise. I 3d-printed them in ABS, but there is no reason why it would not work in, say, PLA.
Note that yellow cap is special and requires different wrench pattern for it. A had to use the cap from the previous battery because it has carefully drilled hole in it where water level sensor goes in.