Five Battery Sizes Now Fit Most New Cars

There are around 30 BCI battery group sizes in our dataset. Most of them barely matter any more. Measured across the vehicles automakers actually build, the battery aisle has narrowed sharply - and the winners are not the sizes American drivers grew up with.

The finding

From the mid-2000s onward the trend is unbroken: the five most common group sizes went from covering roughly two thirds of vehicles to 91.2% in 2025-2026. The top three alone now cover 69.2%. Fewer sizes are doing far more of the work.

The more interesting part is which sizes won. In the early 2000s the leaders were Group 24F, 35, 78 - American and Japanese sizes. Today they are Group 48, 94R, 47. Groups 47, 48 and 94R are the BCI numbers for the European DIN sizes H5, H6 and H7. American cars, in other words, quietly standardised on European battery formats - a side effect of global platforms replacing regional ones.

What it means for you

Practically, it means the odds are good your car takes one of a handful of sizes - and that a shop is more likely to have it on the shelf. It does not mean batteries became interchangeable: the group size still has to match, and now that AGM is the majority fitment, getting the type right matters more than it used to. Look up your exact year, make and model before you buy.

Methodology

Based on 3,072 verified vehicle-year battery fitments across 250 models, compiled and cross-checked against manufacturer and retailer fitment sources, with the source and verification date shown on every vehicle page.

Why concentration, not a count of sizes: the obvious way to measure this would be to count how many distinct group sizes appear each period - but that number falls automatically whenever a sample is smaller, which manufactures a "consolidation" trend out of nothing. We measure the share of vehicles sitting on the most common sizes instead, which does not depend on sample size. Periods with fewer than 50 data points are excluded.

Scope: a large sample of popular US-market models, not a census of the US fleet, weighted toward the vehicles people look up. Factory fitment, not sales-weighted market share - and the earliest period carries the smallest sample, so read the trend from the mid-2000s onward.

Free to cite with attribution to GarageDex. Questions about the data? Get in touch - we are happy to share detail.