This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
When recharging the cells of a wet battery it is best to procure the best grade of sal ammoniac, the kind that is put up in boxes having a sufficient amount for one cell. Then, before putting the solution into the cell, melt some paraffin used for preserving purposes and dip the upper end of the carbons, zinc, and the glass jar in it. This will apply a coat of insulating wax that will prevent any white deposit from working up on the parts and corroding the binding posts, or terminals.
The cells are then filled in the ordinary manner, after which the carbons and zincs are raised just far enough to admit a layer of common machine oil, about % in. thick. The oil not only prevents evaporation but aids greatly to keep the uncovered parts from corrosion. - Contributed by L. R. Kelley, Philadelphia, Pa.