A car battery goes bad primarily due to a combination of chemical degradation, physical damage, and lack of maintenance. The most common cause is sulfation, where lead sulfate crystals build up on the battery plates, preventing them from holding a charge. Other key factors include excessive vibration, extreme temperatures, and simply reaching the end of its natural service life after numerous charge cycles.
Common Causes of Car Battery Failure
| Failure Cause | Description | Typical Impact on Lifespan |
|---|
| Sulfation | Lead sulfate crystals harden on plates, reducing charge capacity. | Can reduce life by 50% or more if left unresolved. |
| Deep Discharging | Frequently draining the battery below 80% state of charge. | Each deep cycle significantly shortens overall lifespan. |
| Heat Exposure | High under-hood temperatures accelerate chemical reactions and water loss. | For every 15°F over 77°F, battery life is cut in half. |
| Vibration | Physical shaking can damage internal plates and connections. | A major cause of premature failure, especially in rugged vehicles. |
| Corrosion | Buildup on terminals increases electrical resistance. | Prevents proper charging and starting, leading to strain. |
| Parasitic Drain | Small, constant electrical draws from accessories when the car is off. | Slowly drains the battery, leading to chronic undercharging. |
| Low Electrolyte | Water evaporates from the cells, exposing plates to air. | Exposed plates sulfate immediately and are permanently damaged. |
| Old Age | Normal wear and tear from the charge/discharge cycle. | Most batteries last 3-5 years under ideal conditions. |
Think of a battery as a chemical engine. Every time you start your car, it uses a massive burst of energy. Recharging reverses the chemical reaction, but it's never 100% perfect. Over time, this inefficiency leads to the permanent crystal buildup we call sulfation. Short trips are particularly hard on a battery because the alternator doesn't have enough time to fully recharge it after the large draw from starting.
Extreme cold thickens engine oil, making the engine harder to crank and demanding more from the battery. Paradoxically, intense heat is even more damaging, as it causes the battery's fluid to evaporate and accelerates internal corrosion. A battery that's several years old and struggling in the winter likely didn't fail because of the cold; the cold simply exposed the weakness that heat created the previous summer.
