Here’s what causes a car battery to die without warning

The 5 things that cause a car battery to die without warning

Normally, a car battery gives you some warning symptoms that something’s wrong. Slow cranking is the most common one. But sometimes, a car battery dies with no symptoms and no warning. Here are the 5 most common causes of sudden car battery failure:

1) Plate shedding creates a short circuit

An internal short circuit caused by battery plate shedding instantly kills the battery

Flooded lead-acid batteries are made from individual plates that are formed in a grid pattern. The grid pattern is designed to allow for the maximum acid-to-plate contact area. The lead material on the positive plate can flake off or “shed” due to normal expansion and contraction during charging and discharging cycles. Over time, the shedding plate material builds up, forming a brown mud-like sediment at the bottom of the battery case. This happens on all batteries and is considered normal aging.

To prevent early failure, battery manufacturers design the case with a built-in sediment trap at the bottom. If the sediment level builds to the point where it touches a positive and negative plate, the battery shorts out and completely drains the battery. That’s precisely what happens when your car starts just fine one minute and is totally dead the next time you try to start it.

Short circuit caused by battery plate shedding

2) Parasitic draw can also cause a car battery to dith with no warning

Modern vehicles are equipped with various computer systems that constantly draw a small amount of power even when the engine is off. These components include the engine control module, anti-theft systems, and the remote keyless entry system. They’re all designed to shut down and go into “sleep mode” 15-45 minutes after you shut off the engine. Once they’re shut down, they draw very little power. The sleep mode power consumption is so small that your battery can power them in that state for 4-6 weeks. But sometimes a module doesn’t go to sleep and keeps drawing power until your battery is dead. That’s referred to as a parasitic battery drain and the only way to find the root problem is to perform tests on the electrical system. To learn how to perform a parasitic battery drain test, see this post.

3) Temperature extremes can damage your car battery

Most people don’t realize that heat is the number one killer of car batteries. If you’ve had a recent hot spell and suddenly your battery is dead, it was most likely heat related.

4) Age can cause a car battery to fail without warning

All batteries have a limited life span. Even if a battery seems fine and is functioning adequately, it might be nearing the end of its life. In such cases, the battery can fail suddenly and without any apparent symptoms because it has already been weakened by age-related degradation.

5) Long periods of non-use can cause a car battery to die with no warning

Until the Pandemic hit, most people didn’t realize the harmful effects of not driving. But several months into the pandemic, many people were shocked to discover that their fairly new batteries were dead. Here’s why that happened.

All batteries self-discharge, even the AA batteries in your kitchen drawer. But car batteries self discharge at a faster rate than household batteries. As they lose their charge, they start to develop a buildup of sulfate crystals on the lead plates. This buildup is called sulfation and it dramatically reduces the battery’s ability to produce power. If left unused for long periods, sulfation is irreversible and the battery must be replaced.

Long term sitting also causes acid stratification; where the heavier acid portion of the acid/water mix falls to the bottom of the battery. The stronger concentration of battery acid deteriorates the bottom portion of the plates, rendering them unable to produce power.

6) Long term current usage with the engine off can cause a battery to die without warning

Leaving the headlights on for an extended period or using power-hungry accessories while the engine is off can cause an otherwise healthy battery to fail.

©, 2023 Rick Muscoplat