Does Having a Bigger Battery Hurt Your Car?

by Don Bowman

Most vehicles have limited space for batteries, so in many cases a larger size, from a physical standpoint, may not work. The problem in most cases is that the terminals will contact the hood and short out the battery or the physical dimensions just will not work. Battery physical size does not mean that the battery has more power or longevity.

Identification: Physical Size

The battery size is printed on the top of the battery as a group number. This group number defines the physical properties of the recommended battery to fit the vehicle in shape and location of the battery posts. It may be possible to install a larger diameter battery; however, a measurement should be made as to the clearance on all sides from obstructions and the battery terminal type and location. If it is a top post battery, the clearance should be measured from the hood, so as to prevent contact of the battery terminals with the hood.

Identification: Battery Power Output

On the top of the battery, there are some important numbers to know. Cold Cranking Amps (CCA): This number is important if living in a cold climate. It indicates the amount of amperage the battery is capable of delivering zero degrees Fahrenheit for 30 seconds. The higher this number is, the longer the battery will crank the engine in cold weather before it dies. Reserve Capacity (RC): This number indicates how long the battery can maintain a 25-amperage draw before dropping below an unusable 10.5 volts. This is particularly important in the event the alternator fails. It is saying it will operate the vehicle on its own without an alternator for this period of time. The higher the RC, the stronger the battery from a starting standpoint. There are small batteries that will put out over 1,000 amps with a good RC.

Identifying a Problem Battery

The battery size recommended for a vehicle is always in excess of what is actually needed. If starting problems are incurred, either the battery has a bad cell or there is another underlying problem. It is easy to check a battery for a common bad cell. As a battery wears down, usually a cell either shorts out or stops producing. A battery will put out 12-plus volts even with a bad cell. The bad cell, however, will dramatically drop the amperage, which will cause a hard start condition. Use a common voltmeter to test the battery. Raise the hood and, with the engine off, connect the leads of the voltmeter to the terminals of the battery, keeping the red lead to the positive terminal and the black to the ground (negative terminal). Have a helper start the vehicle while you watch the voltmeter. If, when the starter is engaged, the voltmeter drops to less than 10 volts the battery is bad. With the engine running the voltmeter should show 14.5 volts. This means the alternator is charging.

Determining the Life of the Battery Remaining

There is a letter followed by two numbers on the side of the battery. These indicate when the battery was produced. If the battery label says it is a 36 or 48 month battery, read the code to determine the life remaining in the battery. The first letter denotes the months. A is for January, B is February and so on. The next three numbers are the day and year.


A larger capacity battery is available for applications such as a high power stereo system or for add-on components. Larger capacity batteries operate applications that take a lot of juice safely for a longer period before charging.

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).