Why batteries go dead and other shocking tales

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Close-up, under-the-hood view of a car battery.

Do you understand how a standard 12-volt automotive battery works? (Photo Credit: CC BY/dave_7/Flickr)

You’ve left the headlights on overnight, and now your car’s engine won’t even crank. However, try it again an hour later and you hear some life or maybe even get the engine to turn over. What’s going on with that 12-volt lead-acid car battery?

How car batteries work

Most standard auto batteries work in the same way. The combination of sulfuric acid with lead plates works to store chemical energy. When you turn the key to draw electrical power, acid runs over the lead, creating a charge. The plates hold charge that is depleted and replenished (sometimes recharged from an external source) over the course of however many cycles the battery can stand before it can no longer hold a charge. Under average use, most car batteries last three to six years, although heavy use – hard winter storage, not keeping the engine full of distilled water, etc. – can wear out a new battery within two years.

Batteries, back from the dead

How Stuff Works explains why an auto battery can go from seemingly dead to among the living after a rest. Because a battery is self-recharging, the earlier attempt to crank the engine got the process rolling. The hydrogen gas buildup created on the surface of the carbon rod that contacts with the liquid sulfuric acid inside the battery disrupts the reaction necessary to produce electrical power. Once the gas dissipates, the battery appears to come back to life with the next start attempt.

In general, the more demands placed upon a car battery, the faster chemical reaction by-products like hydrogen gas build.

Beware that parasitic draw

Sometimes, even slapping a car battery on a charger or replacing the battery won’t do the trick. An ASE Master Auto Technician, Consultant and Parts Specialist points out in the Automotive.com forums that it’s likely either the battery or a parasitic draw are to blame. Either the recharged or new battery is weak/has a short, or another on-board system/device within the vehicle is demanding undue amperage. If lights are dimming and the battery warning light has been coming on, then a bad alternator is the likely culprit.

Too many jump starts is a bad idea

If you plan to keep your vehicle in storage for a long period of time, it isn’t a good idea to jump start it every year after the snow melts or the sun goes to bed. That kind of wear and tear kills the life of a battery. Popular Mechanics suggests either using some form of portable solar panel charger long term, or even having a battery disconnect switch wired into the ground cable to minimize parasitic draw that can discharge the battery entirely over long a long winter.

Recycling lead-acid car batteries



How Stuff Works

Popular Mechanics

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