Car Battery Myths PDF Print E-mail

I had to have my car jump started. Will driving my car for 30 to 45 minutes charge up my battery after it’s gone dead?

No. Your vehicles charging system was not designed to bring a flat dead battery back to life. No amount of driving will fully recharge a dead battery. Idling the engine for periods of time will not help either. Surface charging or continuous undercharging will lower the capacity of the battery over time and deep discharges can damage batteries and will shorten their lives. When a dead battery needs to be recharged, the only way to reliably restore it is to use an appropriate multi-stage battery charger. The charger voltage needs to be high enough to mix the battery acid evenly in the electrolyte to prevent ‘stratification’. You will also save wear and tear, and fuel by using a charger to restore the battery to its maximum charge.

I’m a student and my car sits for several days to weeks at a time. Is it normal for a battery to go dead if the car is not driven consistently?

Yes. Batteries have a natural self discharge, plus all modern vehicles electrical systems draw power from the battery, even when the car is turned off. The battery power is needed to keep the computer, clock and radio from losing its memory. Over time the battery will become fully discharged if the car is not driven. The only way to overcome this is to use the vehicle regularly or connect a maintenance charger, which will keep your battery in good condition. Additionally, short stop-start trips, driving in extreme hot or cold weather, and leaving corrosion and loose terminals unchecked all contribute to draining a battery.

My battery went dead three months ago and I've had the car jump started twice. The battery is less than twelve months old, shouldn't it be replaced under warranty?

No. A discharged battery is generally a good battery, unless it’s been continuously undercharged/surface charged. By correctly recharging it using an appropriate charger, it will, in most cases, restore the battery condition and prevent further breakdowns. You should also have your charging system inspected to ensure it’s producing enough power. It’s also possible the culprit draining the battery is a trunk light or accessory left on. Have your battery and electrical system tested by a professional, and if no problems are found, they should be able to recharge your battery so that it will start reliably.

Should I disconnect my battery terminal if I'm going away for several weeks?

No. Disconnecting the battery will affect the cars on board computer systems that require a specific amount of power to run them. If this power supply is interrupted it can cause vehicle operation issues including engine, steering, transmission and security system problems. When you reconnect the battery it may even prevent the vehicle from being started. A fully charged battery should last several weeks without effecting the operation of the vehicle. The best way to maintain a battery on extended holidays is to use a good quality maintenance charger. These chargers can be left connected for indefinite periods, ensuring your car battery will be fully charged while you are away.

Can a dead battery affect fuel economy?

Yes. When a battery is fully discharged, the car’s alternator will try to recharge the battery as best it can. This added load on the engine will use more fuel.

Do I need to service a 'maintenance free' battery?

Yes. Regardless of the battery type, they will all require the terminals to be checked and cleaned if necessary and the alternator charge rate checked. Any corrosive build up on the outside of the battery also requires cleaning, this will reduce the likelihood of the battery self discharging. Once discharged, maintenance free batteries along with all other battery types will require recharging using an appropriate multi-stage battery charger.

A friend of mine says the bigger the cold cranking amps (CCA) the better the battery?

No. Most vehicle manufacturers design electrical systems around a specific size battery. It is now common for manufacturers to use the vehicle computer systems to regulate the power required for normal operation. Generally the electrical system will only use a fixed amount of current from the battery based on the requirements of the starter motor and electrical system. A larger CCA battery supplies only what is required. It will not damage your vehicle, however using batteries with a higher or lower capacity can affect the performance of the battery and if physically the wrong size could potentially cause damage.

I replaced my car battery myself. Now the car won't idle, the radio doesn’t work, and the radio display says ‘code’. Was this caused by replacing the battery?

Yes. Most modern motor vehicles require the battery power to be connected at all times. By disconnecting power from the battery or when the old battery fails, the computer which controls the idle speed can lose its memory and needs to be reset by your mechanic. If the car radio also loses power it may set the security function. For the radio to work, the security code needs to be re-entered. The code should be hand written in the owners manual when the car is purchased, but often is not. If it’s not there, you will need to contact the dealer with the VIN number, or radio serial number to obtain it. Some car radios have personal code numbers set by the owner, if lost it will need to be reprogrammed. When replacing batteries in late model vehicles a ‘memory minder’ must be used to ensure power is kept to the vehicle electrics at all times.

My old battery lasted less than 36 months, is this normal for a battery?

No. While batteries do degrade over time, how long a battery last depends on a number of factors including, the initial construction of the battery, the climate in which the vehicle is operated, how often the vehicle is used, and if the battery and vehicle have been properly maintained. Quality batteries generally have a 60 to 75 month warranty.

I’ve lost the hold down bracket for my battery, do I need to replace it?

Yes. Batteries left loose inside the engine bay can vibrate and cause the battery to fail. An unsecured battery can also fall into the moving parts of the engine and cause damage. Acid can also leak from the battery damaging the engine, components and paintwork. Unsecured batteries can also ‘short out’ on metal parts under the bonnet and cause a fire or explosion. It is important to secure all batteries using appropriate hold down brackets and clamps according to the manufacturers recommendations.

My battery and terminals have a powdery build up on them. My mechanic said they should be cleaned, but everything is working okay. Do I need to have it cleaned?

Yes. All battery terminals regardless of the battery type will corrode over time. The reason this happens is due to electrolysis. This occurs when current is passed through the dissimilar metals used in the battery posts and terminals. This can lead to poor battery connections, which can prevent power from being supplied to and from the battery and lead to a vehicle breakdown. The only way to prevent this is to have the terminals cleaned.

The battery light has come on, so the battery must be faulty, right?

No. The battery or ‘power’ light comes on when there is a problem with the vehicle charging system. In older cars this was called an alternator light. The battery light indicates the car is running on battery power alone. Continuing to drive a vehicle with the battery light on will end in a breakdown and can cause other damage to the car’s electrical system. You should get your car to your mechanic as soon as possible.

I replaced the battery in my car myself and connected the cables the wrong way. I've now connected them correctly and I have no power in the car at all. Shouldn't the car work now they're correctly connected?

No. All modern motor vehicles have a negative to ground polarity. Polarity in electrical current terms is the flow of moving electrons in a direction either negative to positive or positive to negative. By connecting the cables incorrectly, the flow of electrons will be in ‘reverse’ polarity. This can damage sensitive electrical components and destroy fuses and fusible links and potentially cause an explosion from the battery. If your car won’t start, you may need to get the car towed to your mechanic for repair.




Used Cars


[In 2000] Commuters will go to the city in huge aerial buses that hold 200 passengers. Hundreds of thousands more will make such journeys twice a day in their own helicopters. --Waldemar Kaempfert, Popular Mechanics, 1950.

AJ Foreign Auto

130 Cherry Street (Behind Wegmans)
Ithaca, NY 14850
Business Hours: Call for appointment
Show Map

Look for the Star Wars mural!

Read the story of the mural...