Updated · Batteries
What a group size tells you
Group sizes are standard codes, often printed as a BCI group, such as 24F, 35, 65 or 48. Each one sets the outside length, width and height of the case, which side the positive post is on, and the style of terminal.
Two batteries in the same group should drop into the same space and line up with the same cables, even if different companies made them.
Letters and alternate names
The codes carry details worth knowing. When in doubt, the safest match is the exact code on the battery in the car now, as long as that one was correct.
- An R after the number, as in 51R, means the positive and negative posts sit on the opposite sides from the standard layout
- European-style batteries may go by H or L codes; group 48, for example, is also sold as H6 or L3
- Some GM and older domestic cars use side terminals instead of top posts
- Some batteries have both top posts and side terminals so they fit more cars
Why the wrong size causes trouble
A battery that's too tall can touch the hood, and if metal touches the positive post, it can short out. One that's too small can shift around even with the hold-down tight, and vibration shortens its life. With the posts reversed, the cables may not reach, and stretching them isn't safe.
Many European-style cases also have a ledge at the base that the hold-down clamps onto, so a case without that ledge won't stay put.
How to find yours
Some cars accept more than one group size depending on the engine or options. If you're unsure, go with the size the car came with.
- Read the label on the top or side of the current battery
- Check the owner's manual under specifications
- Look up the year, make, model and engine in a battery fitment guide
- While you're there, note the CCA and the type, AGM or flooded
Size, rating and type together
Group size is about fit. It says nothing about how strong the battery is or whether it's AGM. Check all three: the group size, a CCA at or above what the car requires, and the same type the car shipped with.
Share the year, make, model and engine when you call for a mobile battery replacement; that's usually enough for us to bring a battery that fits. The code from your current battery's label helps too.