What is this? (drainage pipe?)

[Ghostrider 310]

If I recall correctly, it's to allow overflow of Sulfuric acid or gasses to prevent the battery from exploding which I have seen but not in 30 years. Be advised, many batteries look sealed but actually have serviceable cells, I know the Interstate my 986 had was accessible as many are. If you allow the fluid level in a battery that can be serviced to go below a lead plate, nine times out of ten it's toast...

[stephen wilson]

Most cars don't need a vent tube because they are in a ventilated area, the engine bay. The boxter battery it in a fairly well sealed space, the "Frunk".