How to buy the right size car battery

A dead car is a drag, but these tips help you buy the best battery to get started again.

Brian Cooley Editor at Large
Brian Cooley is CNET's Editor at large and has been with the brand since 1995. He currently focuses on electrification of vehicles but also follows the big trends in smart home, digital healthcare, 5G, the future of food, and augmented & virtual realities. Cooley is a sought after presenter by brands and their agencies when they want to understand how consumers react to new technologies. He has been a regular featured speaker at CES, Cannes Lions, Advertising Week and the Publicis HealthFront. He was born and raised in Silicon Valley when Apple's campus was mostly apricots.
Expertise Automotive technology, smart home, digital health. Credentials
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Brian Cooley
3 min read

The numbers and letters that make up a battery's BCI number ensure you are getting the right physical size and terminal orientation for your car. It says nothing about the battery's electrical potential, however.


When you car won't start and you need a new battery, you're hardly in the mood for technical research and introspection. BCI numbers, cold cranking amps, internal construction details and warranty caveats come at you in a blur when you just want to pay up and get going again. So before you find yourself in that predicament, spend two minutes to read our concise look at all the things you need to know to buy the best new battery for your car.

Watch this: Get the right new battery for your car

Voltage: This one's easy. Unless your car was made before the 1960s, it uses a 12-volt battery. Even electric and plug-in hybrid cars use a 12-volt battery for starting, lights and accessories, all separate from the giant drive battery that you would't replace yourself.

Size: You need the right physical size to fit both in the battery compartment in your car and under whatever fastener keeps the battery there. No need for a tape measure, just get the BCI (Battery Council International) number off the battery you're replacing. That specifies the industry standard shape you need, out of roughly 70 combinations available for cars.

Terminal position: The BCI number will probably have some letters as well, and they'll help specify where the two electrical terminals are located on the battery. Getting this right ensures your car's battery cables can reach the terminals and not be strained.  

Those are the factors where no decisions are required on your part. Here are the areas where you need to pay attention:

Cold cranking amps (CCA): Think of this as the battery's ability to supply your car's demand for starting power. Enough is enough, but more is better and won't hurt your car. Specifically, CCA reflects the number of amps of 12-volt DC electrical power a battery can supply to the car's starter for 30 seconds at 0 degrees Fahrenheit. Amps are what make a battery "stronger" in a car, not volts, so always get a battery that has at least the number of CCAs as the original factory battery.


CCA is the ability of a battery to deliver the amperage a car needs to start. You can buy too few, but you can't buy too many. Make sure you have at least the number your car's original battery provided. 


Reserve capacity: No, this isn't some secret reserve of charge you can tap into when your car is dead. Reserve capacity is just another way of measuring the battery's single reservoir of charge, in this case how many minutes it can deliver 25 amps of 12-volt DC power at 80 degrees Fahrenheit. Don't sweat it, everyone just goes by the CCA number.

Internal design: Most batteries are a heavy, low-tech box of lead plates suspended in dilute sulfuric acid, and the reaction between the two creates the electrons that flow through the two external terminals. A more modern take on that design is the AGM (Absorbent Glass Mat) battery. It soaks mats of fiberglass in the sulfuric acid solution and sandwiches them with lead plates for a design that is a bit lighter, able to accept and deliver a charge a bit better, and is less prone to leakage or damage from vibration. It's a nice upgrade, but not necessary for most cars.


Batteries will vary in price largely based on CCA rating and warranty length. Make sure you understand the period during which you will get a new battery under warranty and not just a pro-rata credit toward a new one.


Warranty: Car batteries come with warranties ranging from 12 to 72 months, a huge difference in both peace of mind and cost. I've had more than one counterperson at an auto-parts store confide to me that most batteries are the same inside, with warranty and price coupled as more of an insurance product than an internal quality difference. It is possible to make a better battery by using better quality lead, but you have no way of knowing that, so choose the best warranty you can reasonably afford, knowing that it may be stated in two parts: A full replacement term, during which you will get a new battery if yours fails, and a pro-rata period after that during which you will get a sliding partial credit toward a new battery. Ask about both terms before you buy, and keep your receipt in the glovebox to make warranty claims easier. 

Freshness date: Look for this on a label on the battery case, and try to buy a battery that is no more than six months old. Car batteries don't get better sitting around.