Battery Equivalents and Replacements

How Long Does a Car Battery Last?

This simple question requires rather a complicated answer in order to answer it thoroughly.

But for short, a car battery should last at least 2-5 years. Car battery lifespan depends on the battery type and quality of design and construction, battery maintenance, alternator/charger design and quality, environment, driving habits, battery usage, etc.

Published: December 3, 2021.

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Car Battery Lifespan

Generally, car batteries last 2-5 years with most models lasting 3-4 years, after which they must be replaced.

Most car batteries are lead-acid batteries that are designed as starting batteries - they are able to provide strong currents for short periods of time, but they are not intended for deep discharge applications and especially not for cycling applications.

After cranking the engine, starting batteries must quickly accept a charge from the alternator/charge controller in order to be ready for the next engine start, which may come rather quickly, especially in the cars with Stop/Start systems, where the engine is turned Off when the car stops, for example, at red traffic lights.

When the engine is turned Off, the car battery must also provide power for all the electric and electronic loads that are commonly found in modern cars, including car central computer, lights, audio/multimedia, navigation, etc.

As one can see, the car battery is the center of the car's electric system and when the car battery has issues, the car as a system may simply - stop.

Lead-acid batteries may be wet/flooded lead-acid batteries, maintenance-free enhanced wet/flooded lead-acid batteries, Absorbent Glass Mat (AGM), and Gel-Cell batteries.

Most cars come with their batteries under the hood, with or without additional mechanical and thermal protection.

What Kills Car Batteries

For the lead-acid battery to last as long as possible, it must be kept fully charged at room temperature or even at a slightly lower temperature with somewhat reduced performances.

Of course, these requirements are far from what real life has to offer.

Battery Overcharging/Undercharging

Lead-acid batteries have negative temperature coefficients and they must be charged with different voltages at different temperatures - during winter charging voltage must be increased, while during summer charging voltage must be decreased.

Some modern cars feature digital battery charge controllers that take into account battery temperature and charge it according to its temperature - but, this is more the exception than the rule.

Cars that have charge controllers that constantly provide more or less the same charging voltage have their batteries during the winter undercharged, and during the summer their batteries tend to be overcharged.

Note: car battery charging system consists of the alternator and charge controller which range from a diode bridge with few capacitors to an advanced digital charge controller with programmable firmware.

Short Drives - Stop&Go (Stop/Start) Systems

When the engine starts, it pulls plenty of Amps for a very short time.

And when the engine is working, the battery is automatically recharged - the charging current is much weaker than the starting current and it takes some time for the battery to get fully charged again.

Short drives may force the battery to work hard, without enough time to recharge it completely.

For example, if the car pulls 600 Amps for 2 seconds when starting the engine (1200 Amp-seconds), in theory, the battery must be recharged for 120 seconds at a 10 Amps rate to be recharged completely.

Note: 12V alternator in passenger cars may put out up to or even more than 50-100 Amps, depending on the alternator model and the battery discharge level. Of course, some of the current goes into the battery, and the rest goes for lights, electronics, audio/multimedia, etc.

However, in real life, the charging current is not constant and the battery needs somewhat more charge than it provided.

Now, imagine driving the car with the Stop&Go system during a rush hour, with all the traffic lights being red - in such situations the battery works hard.

Fortunately, cars with Stop&Go systems mostly monitor the battery condition and if the battery voltage drops below a certain level, the Stop&Go system is automatically turned Off.

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Vibrations and Mechanical Impacts

Car batteries are sensitive to vibrations and mechanical impacts since they can damage both interior and exterior of the batteries.

The rough and uneven road can significantly increase the mechanical load on the battery and its inner plates.

Excessive vibrations from the engine can also shorten the battery life - inner plates, especially of the wet/flooded lead-acid batteries may be sensitive to such damage.

High and Low Temperatures

High temperatures increase the rate of chemical reactions in the battery, increasing the batteries' self-discharge rate, but also the rate at which the battery deteriorates.

Low temperatures prolong the battery life when the battery is charged properly and decrease the self-discharge rate.

But, low temperatures also decrease the batteries' performances, increasing the strain when the engine is cranked at low temperatures.

Parasite Loads

When the engine is turned off and the car is locked, the battery is nonetheless drained by a security/alarm system, remote lock system, and similar.

Such systems are designed to have ultra-low power requirements, but nonetheless, they do drain some current.

A typical car alarm system in standby mode draws 40-50 mA, but some models go up to 75-80 mA.

An alarm system with 50 mA draw requires 1.2Ah daily, and an 80 mA alarm system requires 1.92Ah daily.

So, if You leave your car for two weeks parked in the garage at mostly room temperature, your car battery will be drained by ~17-27 Ah, which should not be a problem for a modern 70-80Ah lead-acid battery - if it happens occasionally. If it happens regularly, consider getting a good car battery maintainer.

Corroded Battery Terminals and Loose Cables

Wet/flooded lead-acid batteries cause chemical reactions on the battery terminals which increase electric resistance and prevent the battery from providing strong enough currents for engine starting and prevent the alternator to charge the battery properly.

Also, loose cables increase the electric resistance and are sometimes very hard to detect - if You have issues with the engine starting and if everything looks good with the battery, check the connections and if necessary retighten them.

Of course, there are other reasons that may harm the car's battery, but these are the most common ones.

How to Prevent Battery Failure

There are several things that a car driver/user can do in order to prolong the battery life, including:

- extreme temperatures: if possible, park the car in the garage that protects the car from temperature extremes. When parking the car outside during summer, if possible, park the car somewhere in the shade.

- car usage: if the car is seldom used, it is recommended to take it for a drive for at least 30 minutes every week - this varies greatly from the car to the car, of course, but ...

- driving habits: if You tend to drive your car for short drives (a few minutes or so), it is a good practice to take the car every 1-2 weeks for a somewhat longer drive, at least 20-30 minutes. This will give the car enough time to fully charge the battery (which was not empty, of course, but also it was not fully charged!).

- vibrations: properly set hold-down battery hardware prevents excessive vibrations. Also, any protective battery shielding must be properly positioned in its place.

- check parasite loads: if the parasite loads are above 50-80mA, there is something that pulls too much electricity from the battery - check the lights, audio, and similar loads and if they are left turned On, turn them Off. If nothing can be found that drains the battery, take the car to the repair shop so that they can find out the reason.

- check the cables periodically: if the battery terminals are corroded, clean them. Also, retighten any loose cable/wire.

- check the electrolyte level: wet/flooded lead-acid batteries vent out oxygen and hydrogen, thus losing water. If the electrolyte level drops below a certain level, the cells may be left exposed/dry. So, it is recommended to periodically check the level of electrolyte in wet/flooded batteries and if required, to add distilled water - especially during the hot summer days. Or, take the car to the repair shop and let them check the battery.

- mechanical damage: in order to prevent mechanical damage to the battery, slow down on rough terrain/roads and periodically check the car's shock absorbers (this will also make the drive more comfortable in general). Also, be sure to periodically check the engine's mountings - they should smooth out the excessive vibrations from the engine.

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Weak Battery Warning Signs

Before the battery dies or before it gets fully discharged, there are few signs that can warn the user that there is an issue with the battery.

These signs include:

- issues with cranking: engine cranks, but it doesn't start as quickly and smoothly as it should,

- weak lights: when the engine is turned off, the lights are weaker than usual, etc.

- low voltage: some cars feature a car battery voltmeter and if that voltmeter shows, while the engine is Off, voltage below 12V, the battery is seriously discharged.

Also, the newer cars monitor the battery voltage and signal to the users when it is time to charge the battery - meaning, turn Off the music, turn On the engine.

Install the Correct Car Replacement Battery

When the battery is about to die, replace it.

When changing the car's battery, there are a few things to check:

- both old and new batteries must be of the same physical size,

- both batteries must be of the same chemistry (unless You are certain that the new battery chemistry is compatible with your car's electric system) and voltage,

- new battery must have the same or better capacity and Cold Cranking Amps (CCA) rating,

- both old and new batteries must be of the same type (starting, dual-purpose). In some situations, it is possible, even recommended, to replace starting battery with a dual-purpose battery and vice-versa.

- both batteries must have the same battery terminal type and orientation, or adapters must be used.

Modern cars don't like too much to be left without power not even for the shortest amount of time - if You are unsure about your car or You are unsure about car battery replacement, take your car to the nearest certified car mechanic and let them replace the battery properly.

Car Battery Frequently Asked Questions (FAQ)

Here are some of the most common questions about car batteries:

What is a car battery group number?

Car battery group number or BCI number is the number that is assigned to a certain battery size/type.

What is a Cold Cranking Amps rating?

Cold Cranking Amps or CCA rating is the maximum current that a new fully charged, 12V battery can deliver for 30 seconds, with the voltage not dropping below 7.2V, at 0°F (-18°C).

Put simply, a CCA rating describes the battery's ability to crank the engine.

What is the average lifespan of a car battery?

The average lifespan of a car battery is 3-4 years.

Should I replace my car battery before it dies?

Personally, yes - one should replace the battery before it dies after it shows some signs of age like issues with rankings, dimmed lights, and similar.

How much current does a car alarm draw?

In standby, car alarms draw between 40 and 80 mA - if the parasite load is larger, check the car for turned on lights, devices, and gadgets. If nothing can be found, take the car to the repair shop.

How many amps does a 12v alternator put out?

On average, passenger cars come with alternators that are able to provide 50-150 Amps when the battery is rather discharged - some energy is stored in the battery, some is used for lights, electronics, audio/multimedia, etc.

How many amps does it take to start a car?

Passenger cars usually require 400-600 Amps, while larger SUV vehicles may require 700-1000 Amps, depending on the engine size and type - diesel engines require more power due to the larger compression ratio.

Few Final Words

car battery 1A car battery is in the center of a car's electric system - treat it as it deserves, and it will serve You for years to come.

But, if the battery starts to show signs of age, don't wait too long with the battery replacement.

And when You go for a new battery, don't go cheap - a good battery is not a cheap battery, but it can save You lots of headaches later.

And if You are unsure about your car's battery, take the car to the repair shop and let them check the battery and if required, let them replace it for You - better safe than sorry.