Rick's Free Auto Repair Advice

Causes of Car battery failure

Six Main Causes of Car battery failure

Car battery life has decreased over the past few decades as electrical loads have increased (heated seats, more powerful sound systems, infomatics) and more cramped underhood engine compartments that heat the battery. In fact, if you get four years out of your car battery, you’re doing well. But there are many things you can do to cause your car battery to fail early. I’ll detail the six main causes of car battery failure here.

Car Battery Failure Cause #1: Sulfation due to non-use

Even without any electrical draw from the vehicle’s computers, automotive lead-acid batteries lose about 5% of their charge per month of non-use. That’s just the nature of the chemistry. When you add in the amount of power drawn by the computers, even when they’re in minimal current draw “sleep” mode, a typical car battery will lose enough power in 4-6 weeks to cause a no-start condition.

Leaving a lead-acid battery in a discharged state for long periods causes the formation of sulfate crystals on the battery’s internal plates. The longer the discharge period and the lower the state of charge, the more solid the crystals become, causing permanent battery damage that can’t be reversed through charging.

Car Battery Failure Cause #2 Poor Maintenance

Good battery post-to-terminal contact is critical

corrosion on these battery cable

Look at the corrosion on these battery cables. And you wonder why it won’t start?

to maintaining a proper battery charge level. Corrosion between the battery posts and terminals increases electrical resistance and heat, which prevents the battery from fully recharging. When battery terminals have white or blue/green corrosion, your car’s alternator has to work harder to maintain proper charging and the battery is often in a slight state of discharge. Cleaning your battery terminals and wiping down the top of the battery case greatly increases battery life.

Car Battery Failure Cause #3 Heat damage

Most car owners think that cold weather is what kills batteries. In fact, it’s the opposite. While your car battery may fail to start your car in winter, it was most likely severely damaged during the preceding summer. Excessive heat from storage in the engine compartment or failure to re-install a car battery’s heat shield will cause the chemical reaction to increase and damage the lead plates.

Car Battery Failure Cause #4 Vibration damage and mechanical damage

All car batteries on held in place with battery hold-down devices. Over time these brackets tend to corrode and fail. When they can no longer hold the battery in place, the hold-downs must be replaced. If a car battery is allowed to shake free or bounce, the movement will permanently damage the plates and dramatically reduce the battery’s life.

Car Battery Failure Cause #5 Incorrect charging

Charging a car battery at too high a voltage, for too long, or at too high a current rate can cause the battery to fail early. Overcharging causes overheating, resulting in plate warp/short circuit as well as outgassing and a permanent loss of water. Once the top of the plates is exposed to air, the battery is ruined.

A faulty voltage regulator, faulty alternator or corroded terminals resulting in incorrect charging can dramatically reduce car battery life.

Car Battery Failure Cause #6 Multiple episodes of deep discharge

Using electrical power from your car battery while the engine isn’t running (lights left on, using a laptop) can cause deep discharge. A car battery can handle some deep discharges and recover from them. But repeated deep discharge causes damage that can’t be fixed by recharging.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat


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