Understanding how a car works is a daunting task for the common Joe, who watches even the smallest and seemingly insignificant of component failures stopping his car to a grinding halt, adding to the whimsy and mystic of the subject. Naturally, if a topic or concept is not very well understood, people can fall prey to all sorts of rumors and myths that spread from generation to generation, and the question of a car battery draining on a concrete floor is one of them.
Before we dwell into the details, the myth has some historical basis. When the concept of batteries first arrived, they came in wooden battery cases and a glass jar with the battery inside. So putting it on the floor (of any material) meant that the wood would be exposed to moisture, leading to swelling up fracturing the glass and causing it to leak the acid.
This cause and effect learning continued with the hard rubber battery cases, where the substance was porous enough to make the battery acid seep through it and form a conductive path through the damp concrete, leading to the drainage.
But you are sadly mistaken if you are tempted to apply the same logic to today’s batteries, which are made of sturdier plastic that is not porous or prone to cracking at the mere exposure to a little moisture. Along with that, the technological advancements have improved the seals around the posts and the vent systems by a multifold. Thus we need not worry when storing the batteries, except for the temperature of the storage. The problem of car battery electrolyte leakage and charge migration has been all eliminated altogether!
Battery manufacturer Yuasa have this to say,
“Nowadays, containers are made from a solid plastic that does not allow any current to flow through it, so the batteries do not discharge, even if they sit in a few inches of water.”
Interestingly enough, many experts such as Car Talk’s Click and Clack think that storing car batteries on concrete floors might actually be a great idea because the cold concrete can help slow down the self-discharge (leakage) rate.
The bottom-line: A battery’s discharge rate is only affected by its age, the outside temperature and the constituents of the battery.