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Car battery failure — 7 most common causes

Car battery failure causes — the 7 most common causes

Car battery failure cause #1 — Persistent state of low charge from non-use or short drives

All batteries self-discharge when not used

Car batteries are no different, they self-discharge at the rate of about 1% per day when not used. In addition to the self-discharge rate, auto computers draw a small amount of power 24/7 to retain memory and listen for commands from your keyless entry remote. Between the self-discharge and current draw from computers, most car batteries are severely discharged after about 30-days of non-use (less in cold weather).

Long periods of non-use cause permanent car battery damage

The longer it sits unused, the more it will discharge and become sulfated. When left unused long enough the sulfation becomes irreversible, rendering the battery useless.

Long periods of non-use cause acid stratification

Car battery electrolyte is a mixture of sulfuric acid and water. When a car battery sits for long periods of non-use, the sulfuric acid settles to the bottom of the battery and begins to eat away at the lead plates. That damage is irreversible.

Short trips use more power than the alternator can put back in

If you don’t drive often and then take short trips, your vehicle’s charging system won’t run long enough to replace the power lost due to starting. What’s even worse is if you start the vehicle, turn on headlights, blower motor, defogger, or heat seaters, and then drive a short distance. In effect, you’ve drained far more power from the battery than the charging system can replace. Repeat this several times over a period of weeks and you’ll deplete the battery’s charge even faster, causing sulfation and permanent damage.

Car battery failure cause #2 — failed charging system

A failed alternator can cause a battery to drain completely. If you continually jump-start the vehicle without diagnosing and fixing the charging system, you’ll permanently damage the battery

Car battery failure cause #3 — corroded connections

Corrosion on the battery posts and terminals causes excessive resistance which results in poor charging system operation and a discharged battery. Checking and cleaning battery terminals prior to cold weather is a good preventative measure. See this post for more information on cleaning car battery terminals.

Car battery failure cause #4 — lights left on

Leaving lights on all night can completely drain a car battery. Car batteries can only survive one or two of these events, and even then, the severe discharge causes some damage. In other words, a car battery never fully recovers from a complete drain.

Car battery failure cause #5 — parasitic drain

As mentioned above, all car computers draw a small amount of current 24/7. But that low draw only happens after the computers enter a “sleep mode” after 15 to 45 minutes of non-use. However, when a computer module fails, it can remain in “awake” mode full-time and drain your battery completely in as little as a few hours. If you have to jump-start your car every morning, but it will start on its own in between, chances are you have a parasitic battery draw from an awake computer module. See this post on how to diagnose a parasitic battery drain problem.

Car battery failure cause #6— Vibration

Battery hold-down devices are there for a reason. They prevent the battery from bouncing and vibrating; the kind of movement that can damage the lead plates. If your battery doesn’t have a hold-down device, you’re dramatically shortening its life.

Car battery failure cause #7 — Extreme temperatures

A car battery produces power through a chemical reaction. That reaction speeds up in hotter conditions and slows down in cold conditions. High underhood temperatures are the #1 killer of car batteries. Most people think that cold weather kills batteries. Not true. The numbers show that more car batteries fail in hot weather climates than cold weather areas. Even in more moderate climates, battery analysis shows that most batteries are damaged in summer, but the damage doesn’t show up until the weather turns cold. That’s because even a “good battery” produces 35% less power at 32°F (because of reduced chemical activity when cold). At 0 degrees, battery output is 60% less. When a battery is already compromised from high heat, it’s no surprise that it fails completely when cold weather arrives.

© 2021 Rick Muscoplat

Posted on by Rick Muscoplat

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