For modern car batteries with polypropylene or polycarbonate plastic cases, placing them on concrete has no measurable effect on charge level. The plastic is a non-porous electrical insulator and does not create a discharge path. Multiple battery manufacturers and fact-checkers confirm this for batteries made in the last several decades.

Modern batteries' self-discharge rate is the same regardless of surface — concrete, wood, or a shelf. The plastic case prevents any conductive path from forming between cells and the floor. One informal science-fair experiment also found no measurable voltage difference between batteries stored on wood vs. concrete over a week.

The claim applies accurately to modern car batteries with hard plastic shells. However, it would have been false for earlier battery types (wooden-cased, rubber-cased, or steel-cased designs) that were genuinely susceptible to moisture from concrete floors causing discharge. This historical context is why the myth persists today.

While concrete itself causes no discharge in modern batteries, there is a minor indirect concern: dirt and grime on top of the battery case can create a conductive circuit between terminals, causing slow self-discharge. This is not caused by the concrete per se, but storage conditions (dust, grime, terminal contamination) remain a real, if minor, threat regardless of surface. The word 'zero' is therefore a slight overstatement.

Temperature differentials from a cold concrete floor have been theorized by some engineers to create minor internal voltage differences across battery cells, potentially causing slight discharge. However, this effect is not empirically well-established for modern sealed batteries and most authoritative sources do not treat it as a meaningful real-world concern.