Battery Equivalents and Replacements

Why Does My Car Battery Keep Dying?

Depending on the car use, climate, the battery quality, the quality of the car's battery charging system, and a few other things, the car battery may last on average 2-5 years, after which, it should be replaced with a new one.

Before the battery fails, it may show a few signs of impending failure. However, from time to time, the car battery fails much more often than the typical every 2-5 years and people wonder why?

Published: April 4, 2022.

car engine 1

There are many reasons why a car battery may fail and these are the most common ones. Of course, other less common reasons can cause a car battery to fail, but also there may be several reasons present that can cause problems.

Headlights Or Interior Lights Left On​​​

This is a classic reason why a car battery failed - the lights were left On for several hours or overnight and the battery is discharged.

But, although car batteries are starting batteries and although they are not intended for cycle use and low discharge conditions, the discharged battery doesn't automatically mean a permanently failed/damaged battery.

If the battery is relatively new, but it is discharged too much to be able to crank the engine, start the car using another car or car jump starter and let the car's charging system recharge the battery by taking a longer trip of at least 1-2 hours.

Although most modern cars feature alarms that warn the users that the lights are still On or the lights are automatically turned Off, leaving the lights On is still a very common cause of dead car batteries.

Excess Parasitic Drains In The Electrical System

When the engine is turned Off and the car is locked, the battery is still continuously being drained by the security (alarm) system, remote control system, and similar.

The electric load of these systems is very low and standard car batteries generally can provide power for weeks and still be able to crank the engine safely.

For example, if the security and remote control systems draw 25 mA and the car is left for a week, the battery will be discharged by:

C (Ah) = I (A) * T(h) = 0.025A * (7 * 24h) = 4.2 Ah

So, if the car has a 70Ah car battery charged to 95% of its nominal charge, after a week, the battery will still have:

C (Ah) = 70Ah * 0.95% - 4.2Ah = 62.3 Ah

which is still 89% of the battery's nominal capacity.

However, if the parasite drain is significantly increased for who knows what reasons and the car is left for a longer period of time, the battery can be seriously discharged and unable to crank the engine.

Note: for the car battery to last a long time, it should be kept charged all the time since it is not intended for (deep) cycling applications.

For example, the car electrical system was modified and the parasite load is increased from 25 mA to 350 mA. So, if the car has a 70Ah car battery charged to 95% of its nominal charge, after a week, the battery will only have:

C (Ah) = I (A) * T(h) = 0.35A * (7 * 24h) = 58.8 Ah

C (Ah) = 70Ah * 0.95% - 58.8 Ah = 7.7 Ah

which is only 11% of the battery's nominal charge - hardly that this battery will be able to crank the engine, especially if it is a colder time of the year.

If Your battery regularly fails and the lights were not left On, but the car is regularly being parked for a week or so, check the parasite drain.

car interior

Charging System Problems

A car's charging system consists of the alternator and the charge controller which may range from a simple diode bridge and few capacitors to the advanced microprocessor-controlled charge controller.

If the charging system fails completely or even partially and the battery is not being charged properly, the battery will not be able to crank the engine.

Modern cars are computers on wheels and they usually signal if there are issues with charging voltage and/or current.

But, if the battery fails and even if the car monitoring system doesn't warn about the charging system issues, check the alternator and the battery voltage when the engine is On and Off, just in case.

Extremely Hot Or Cold Temperatures

Lead-acid batteries are still the most common car batteries in use and they feature a negative temperature coefficient, which means that at low temperatures the lead-acid batteries should be charged using higher voltages, and at high temperatures, the lead-acid batteries should be charged using somewhat lower voltages.


When the batteries are not charged using their "ideal" charging voltages, their lifespan is shorter.

Thus, it is highly recommended to park the cars in garages, especially during extremely hot and extremely cold days - such climate can significantly shorten the car battery lifespan.

Electrically Taxing Modifications

Car electric systems are designed to provide plenty of electric energy for standard cars' electric loads.

However, many users modify their cars by adding stronger speakers and amplifiers, stronger lights, and similar.

All those additional electric devices and gadgets increase the load on the battery, alternator, and the rest of the electric system, causing them to fail prematurely.

If your battery is failing regularly and You do have a car with a modified, for example, sound system, check the way the sound system is connected and what are its actual electric requirements.

Corroded Or Loose Battery Connections

Lead-acid batteries, even the spill-proof AGM and Gel-cell batteries produce a faint vapor of water and sulfuric acid which can react with the battery terminals and wires, increasing the electric resistance between the battery and the battery wires.

corroded car battery 2

Also, if the wires are not connected firmly to the battery or they got loose over time, the electric resistance between the battery and wires may be large enough to prevent the battery from cranking the engine properly.

In this case, the battery itself is good, but due to other reasons (increased electric resistance), it can't perform properly.

Too Many Short Trips

One of the reasons why the battery may fail prematurely is taking too many short trips in a short period of time, especially if the car was parked for a longer period of time.

When the engine starts, it drains a huge current for a short period of time.

As the engine revs, the alternator starts to charge the car battery with a much weaker current.

If everything is alright with the car's charging system, it takes a really short period of time to completely recharge the car battery with enough charge that was needed for a single crank.

So, many short trips should not "discharge" a healthy battery connected to a healthy charging system.

But, too many short trips increase the load on the battery and it may fail simply because it works heavily.

car battery

Similarly, for the cars with "Stop&Start" systems, ordinary car batteries are not good enough since such cars require high-quality batteries that are able to provide strong currents and that are able to accept strong charging currents very often.

car pull over mLong Story Short: Car batteries are replaced regularly every 2-5 years because they lose their ability to crank the engine.

However, if the battery starts to fail more often, then one should find out exactly what is causing the battery to fail.

When/if the battery starts to fail more often (two times in several weeks/months is a sign that something is not alright with the car) take your car to the nearest workshop or authorized dealership and let them test the car and find out what is the reason or reasons why your car battery fails often.