8 Things That Can Kill Your Car Battery

8 Things That Can Kill Your Car Battery


This blog post will focus on eight common reasons that can cause a battery drain. Battery age, human error, loose connectors or corrosion, poor alternator, short drives, parasitic draws, extreme temperature and bad starter motors or ignition switches can all “kill” your car battery.

First, we need to define what killing a battery really means. There is a difference between a discharged battery and a dead battery. 

“Dead” has two meanings when used to describe a rechargeable battery:

  • It either means its charge has been drained and it cannot start the car unless recharged
  • or it means that the battery can no longer maintain the required amount of charge for a suitable amount of time as compared to a new battery

Occasionally, the power in your perfectly healthy battery will go so low that it cannot start your car. We say the battery has been discharged. This doesn’t always mean that you need to buy a new battery. It just means that something has drained the power out of the battery and this power needs to be replaced. You can recharge the battery up to 90-100% health and be back on the road in no time at all.

However, sometimes no amount of charging will bring your battery back to good health. Sometimes, after getting a 100% charge, a battery may still not start your car or will start, but run down quickly and refuse to start after the car is parked for a short time. This is the proverbial dead car battery. Throw it away and get a battery replacement. It will just give you a headache.

Your battery is old

165385836551235945902 old car batteries optimize


Your car’s battery could last between three to five years if you take care of it properly. After some time the chemistry of a battery begins to change and it’s unable to keep a full charge for long. Repeated charging will not able to fully reverse the chemical process by which sulfate crystals are converted back into sulphuric acid. Eventually, one or more battery cells may stop functioning completely. This will cause a drop in voltage that will not be helped by recharging the battery.

Human Error

165385844117140557060 driver hand adjusting headlight level switch and car headlight brightdouble exposure automotive concept optimize


You’ve probably done this at least one time in your life – you come home from work tired and not really thinking and left the headlights or cabin lights on. Overnight the battery drained, and in the morning, your car wouldn’t start. Many new cars warn you if you leave the headlights on overnight, but may not have warnings for other electrical components.

Remember to remove your keys, turn off every light and make sure your trunk, glove box, and doors are fully shut and locked before getting out of the car.

Your battery connections are loose or corroded

165385847044331191658 rust and dregs hang and damege battery optimize


Battery connections that are loose or corroded can drain your battery and damage other electrical components in your car. Poor connections are a major cause of battery drainage.

Does tapping the top of your terminals with a spanner or rock make it easier to start your car? If yes, then remove your battery terminals and check for corrosion or loose battery cables. Whitish or greenish powder or crystal on top of your battery terminals are signs of corrosion.

Corrosion can reduce the flow of electrical current. A loose battery cable will cause a power leakage that will reduce the power from the alternator to charge up the battery. It will also reduce the power to the starter motor, which will start the vehicle. To avoid this problem, clean the battery terminals every few months with soapy water or a solution of baking soda. Then apply petroleum jelly to reduce further corrosion. Note that rapid and persistent growth of corrosion crystals on the positive battery terminal is a sign of significant parasitic load.

The battery isn’t charging while you drive

16538585018108594450 engine optimize


Your car depends on your battery to get started. When your car is running, your battery needs an effective alternator to maintain its charge. A bad alternator won’t be able to recharge your battery, making it difficult to start your car even though you’ve just been driving!

Your car may need an alternator replacement if it doesn’t start when you turn the key. Alternators can fail because of a bad diode or a bad regulator. However, a torn fan belt or a loose serpentine belt caused by worn-out tensioners can also prevent your alternator from working properly.

You’re taking too many short drives

16538585353327790430 car garage optimize


Cranking the engine takes a lot of energy from the battery. But when the engine is running, the alternator charges the battery. Short trips do not give the alternator enough time to fully charge the battery. This could lead to shorter battery life.

Something is causing a “parasitic draw”

165385858157427973758 male hand changing the radio station on car lcd infotainment screen optimize


A Parasitic draw is caused when some electrical components in the car drain battery power above normal levels and discharge the car battery too quickly. There is no actual rule for how quickly is too quickly, but most auto electrician would agree that it is not normal for a fully charged battery to be drained if the car is parked for less than two weeks.

Electric components in modern vehicles such as internal lights, glove box lights, exterior lights, dome lights, power locks, power doors, USB ports, automatic windows etc all put a heavy load on the car battery. Short circuit, bad relays, defective fuses and faulty motors in any of these components can cause parasitic drains.

When the engine is running, the alternator charges the battery. But when the engine is turned off, the alternator does not charge the battery. Even when your car is turned off, the battery should be fine for many days before it loses charge completely.

However sophisticated and numerous electrical systems in your car rely on battery power to keep functioning even when the car is turned off. Your radio presets, seat position memory, security alarm and many other electronic components all continue to drain your battery while the car is off. This is called a parasitic draw.

Poor installation of alarm systems, sub-woofers, car amplifiers, fog lights, radio players and other aftermarket electronics can become parasitic drains that slowly discharge the battery.

Remove the negative terminals from your battery if the car would be parked for more than the month. This will reduce the discharge rate of the battery and can keep a fully charge battery functional for two weeks to six months depending on the temperature of the surroundings.

It’s extremely hot or cold outside

165385864982318911870 closeup of man under bonnet with starter cables optimize

Extreme temperature: either too hot or too cold can affect the condition and lifespan of your battery. Your car’s battery needs to be checked regularly during poor weather.

Warm weather causes batteries to lose their charge faster than cold weather does. Heat also affects the life span of batteries.

On the other hand, cold temperatures slow down chemical reactions in the battery and reduce the amount of power that the battery can produce. A battery blanket can heat your battery so that it can produce enough cranking capacity to start the engine.

Bad ignition relay or starter motor

165385873469230920830 woman s hands hold the key for starting the car optimize


The starter is an electrical motor that cranks the car’s engine. It’s under the hood, usually in the lower part of the engine compartment, near the transmission. The ignition switch is a set of electrical contacts that activates the starter and is usually found on the steering column. Problems with any of these components will drain your battery and you won’t have any power left to start the car.