Walk down a battery aisle and you'll see a wall of codes: 24F, 35, 48, H6, 65, 94R. On the label, more numbers: CCA, RC, Ah. Here's what they mean and which ones matter for your car.
Group size: the physical fit
The group size is a standard that sets a battery's length, width and height, and where the positive and negative terminals sit. In North America, the Battery Council International (BCI) group numbers are the most common. Some batteries also carry European-style codes like H6 or H7 for the same idea.
Why it matters:
- It has to fit the tray and the hold-down. A battery that's too small can slide around and vibrate itself to death. One that's too tall can touch the hood, which is a short-circuit risk.
- The terminals have to line up with the cables. Some sizes come in two versions with the terminals reversed. The "R" in a code like 94R or the "F" in 24F often marks that difference. Get it wrong and the cables won't reach, or will be stretched across the top of the battery.
Your owner's manual lists the correct group size, and so does the label on your current battery, as long as the last person who replaced it got it right.
CCA: starting power in the cold
Cold cranking amps measure how many amps a battery can deliver for 30 seconds at 0°F while staying above a set voltage. It's the number that predicts how well the battery will start the car on a cold morning.
Match or beat the manufacturer's specification. In cold climates, going somewhat higher is reasonable. In hot climates, extra CCA matters less than heat tolerance and reserve capacity.
You may also see CA (cranking amps), measured at 32°F. It's always higher than CCA for the same battery, so don't compare a CA number to a CCA number.
Reserve capacity: staying power
Reserve capacity (RC) is how many minutes a fully charged battery can supply 25 amps before it's flat. Think of it as how long the battery can keep the car's electrics running if the alternator quits, or how well it copes with accessories used with the engine off. Higher is better, especially for cars with lots of electronics.
Some batteries list amp-hours (Ah) instead, another way to express capacity that's common on European and AGM batteries.
Type: flooded, EFB or AGM
The size and ratings can match and the battery can still be wrong if the type doesn't. Start-stop cars need an EFB or AGM battery, and cars that came with AGM need AGM. See AGM vs flooded for the details.
The easy way
When you call a local battery tech, they look up the group size, CCA, type and any registration your car needs from the year, make, model and engine, and bring the right battery the first time. No aisle of codes required. Find yours on the locations page.