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WHOLECELLBattery

The charge sheetAugust 3, 2026 · 4 min read

Battery Group Sizes, Explained

What 26R, 31, and the rest of the numbers on a battery actually mean. And how to read a spec plate so you order the right replacement the first time.

Every week someone calls us with a dead battery and no idea what to order. The good news: everything you need is printed on the battery itself. Here’s how to read it.

The group size is the shape, not the strength

A group size (like 26R or 31) is a standard set by BCI, the Battery Council International. It defines the battery’s physical dimensions, terminal placement, and polarity layout. It tells you whether the battery fits the tray and reaches the cables. It says nothing about power.

That’s why two group 26R batteries can have very different price tags: same box, different muscle inside.

  • The number (24, 26, 31, 65…) is the case size family.
  • A letter suffix changes a detail. R means “reversed,” with the positive terminal on the opposite side. A 26R is a 26-size case with mirrored terminals. Put a 26 where a 26R belongs and your cables won’t reach, or worse, they’ll reach the wrong posts.
  • S and other suffixes mark variations like stud terminals. Our 31S-1000 is a group 31 case with stud terminals, common on commercial trucks.

CCA is the strength

Cold cranking amps is how much current the battery can deliver for 30 seconds at 0°F without collapsing. It’s the number that decides whether a cold engine turns over. Our 26R-650 delivers 650 CCA. Right for sedans and light trucks. The 31S-1000’s 1,000 CCA is diesel-and-heavy-equipment territory.

Rule of thumb: match or slightly exceed the CCA your vehicle’s manual calls for. More CCA than spec doesn’t hurt; less means hard starts the first cold morning.

The other numbers worth knowing

  • Voltage. Almost everything automotive is 12V. Golf carts, floor machines, and some equipment run 6V or 8V banks. Check before assuming.
  • Ah (amp-hours) matters for deep-cycle and SLA batteries: it’s how much energy the battery stores, which sets how long it can run a load. A UB1270 is 12V, 7Ah. The workhorse size for alarm panels and UPS units.
  • Terminal type. Top post, side post, stud, F1/F2 spade. Photograph the terminals when in doubt. A perfect battery with the wrong terminals is a paperweight.

Ordering a replacement in 30 seconds

Photograph the old battery’s label and terminals, note the group size and CCA, and send both to your supplier. That’s it. Send them to us and we’ll confirm fit and quote it. Usually within the hour during business hours.