Rick's Free Auto Repair Advice

How long does a car battery last?

When to replace a car battery

The average car battery lasts 4-5 years. Battery companies tell us that only 30% of batteries sold reach the 48-month mark. And they say 80% of battery failures are due to battery plate sulfation build up. I’ll explain what causes battery plate sulfation in this article.

Replace your battery if it’s more than four years old

If your battery is approaching the four year mark, have it tested now so you get a read on its condition. Otherwise it can leave you stranded.

Car battery testing is easy

The old school way to test a battery was to perform a stress test where the battery is loaded to half of its rated Cold Cranking Amps (CCA) for 15-secs. If the battery voltage stayed above 9.6 volts during that period, it passed the test. But that same battery could fail the day after from causes that can’t be spotted by the stress test.

Modern battery testers also conduct a simulated stress test, but they also perform internal resistance tests that can spot weak connections between the bus bar and plates and plate sulfation. These State-of-charge (SOC) testers are far more accurate and predicting future battery life, so you should ask the shop to conduct the test at least once a year.

Here’s how car batteries get ruined

The car battery sits unused too long between charging in hot weather

The car battery sits unused too long between charging in extremely cold

The battery is run down by extended cranking (cranking but the engine won’t fire up) without immediate recharging with a battery charger.

Used in a high heat environment—underhood temperature of 100°F increases internal self discharge.

Low electrolyte level

Improper charging. Using a cheap battery charger can do more harm than good. Recharging a battery requires a specific charging procedure depending on the battery condition. Newer chargers can assess the condition of the battery and apply the correct charging protocol.

Cold weather. Cold weather slows down the chemical reaction that produces power.

Parasitic battery drain. All late model cars draw computer current even when the engine is off. If all computers go into sleep mode, the draw is low (less than 50mA). However, even when all computers are in sleep mode, a 50mA draw can completely discharge a battery in 30-days. If a computer doesn’t enter sleep mode the parasitic draw can discharge a battery within hours. To find the source of a parasitic battery draw, read this article.

Poor battery maintenance decreases battery life

Dirty/corroded battery terminals dramatically

coroded battery terminals

These corroded battery terminals are killing this battery

reduce the amount of current available to start the engine AND reduces the amount of recharging current needed to recharge the battery.


For tips on buying the best car battery, read this article.

If you own a 2000 or newer vehicle, the techniques for installing a new battery have changed. If you don’t follow the proper installation practices, your car may not run at all or may run poorly after a battery change. Read this post on how to install a new battery.

©, 2015 Rick Muscoplat

Posted on by Rick Muscoplat


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