Q. Why can’t you leave your car battery on concrete?
answered by Charles Tom Rauch, RF and Analog System Designer (1983-present)
One of my neighbors and amateur radio friends in Toledo, Ohio was Charles Popper, a senior engineer at Prestolite. Prestolite was a major supplier of OEM and aftermarket batteries. Charlie loved to talk about this issue, and this “concrete floor” thing was one of Charlie’s most hated myths. Charlie really made me feel bad when he saw I had a battery up on 2×4’s to keep it off concrete. I still remember that educational awakening and try to pass it along.
When people see some effect like a dead battery, they make up a cause. Often the cause made up is taken from other folklore with a twist of junk science.
All of the stuff you read about batteries on metal or concrete hurting batteries, once technology was beyond early wooden cased batteries, is junk science. The early wood issue was from deterioration of the wood and mechanical integrity of the battery, not from battery electrical discharge. The only effect is physical.
Unless the case was open cell and actually leaked or seeped with a conductive track, it could not make a conductive path through the case. If it made such a path, the case itself would be problematic even if the battery floated in open air or sat on glazed ceramic.
Lead-acid batteries have been freely mounted in metal housings and trays for years. Metal is far more conductive than even the wettest concrete. They are shipped and stored in cardboard, and acid dampened cardboard is just as bad as concrete, if not worse. The only ill effect is physical deterioration of the container or supporting material.
Lead-acid batteries cannot take long periods of storage without some sort of proper recharge or float maintenance. Lead-acid batteries have a discharge rate roughly between 2% and 40% per month depending on size, type, and construction. Once a battery is deep discharged, even once for a brief period, it loses charge capacity. Let it sit at low charge for a long period and it is ruined. Temperature also has an effect on life.
You can set a battery on a metal ship deck or the concrete floor of a garage, or in a metal box or Teflon container, and as long as temperature is the same the battery will have the same storage life. Let it sit “dead” or on low charge, and it will become useless. Keep it properly maintained and it will have a normal life no matter what it sits on.
addition 7th Oct 2019:
Colder temperatures increase charge retention time, but of course you do not want to freeze the battery. Warmer temperatures increase the self-discharge rate.
Data suggest a typical good fully charged lead-acid with retain 80% of the charge after 18 months storage at 32F (0 C), while 100F temperatures will show the same self-discharge in a week or two.
Many people confuse slower cold weather cranking with battery discharge. Do not confuse slower cold weather cranking with battery discharge. Slower cold weather cranking comes from increased cold engine drag and battery equivalent series resistance increases from slower chemical reaction. The very thing that allows a lead-acid battery to maintain storage charge longer when stored cold, slower chemical reaction, also reduces current capacity while cold. Warm the battery up and current into heavy loads increases dramatically since the battery has actually not “discharged” from cold.