Cold Cranking Amps (CCA) Calculator

Read this as a floor, not a forecast. Each fitted figure is the minimum the calculator returns at the two ends of that displacement band. Beside it sits the middle half of the minimums the source itself prints for engines that size, so you can see how wide the real spread is. The petrol figure is one battery; the diesel figure is a whole-vehicle total, so on a truck that carries two batteries the pair shares it — the 1,385 CCA a 6.7L diesel asks for works out at roughly 693 CCA from each.

Where the two columns disagree, believe the printed one. At the small end the fitted petrol line sits above the middle half, because a straight line through a population whose CCA climbs fast and then flattens over-predicts at both ends. In the 4.1-6.0L diesel band the line sits well below, because almost every diesel that size in the guide is a two-battery truck at 1,500 CCA combined. Below 1.0L the petrol and diesel lines meet, and the guide lists no diesel under 1.6L at all, so a small diesel returns the petrol figure and the calculator says so on the result.

These figures are our own least-squares fit to the original-equipment minimum CCA ratings that Battery Council International publishes for cars and light trucks, as reprinted in the 2011 Cat Batteries Cross Reference Guide: petrol 438 + 46 × litres across 3,197 fitments, diesel 326 + 158 × litres across 131 systems, with two-battery trucks counted as one combined figure. The middle-half columns are the 25th and 75th percentile of the same rows. The guide's petrol rows span 0.8 to 8.4L and its diesel rows 1.6 to 7.3L, which is why the calculator stops there. Check your result against your owner's manual or the original battery label before buying.

The figures above are minimums, and the guide behind them says so in as many words: the cold cranking ratings it lists "are the minimum recommendation for each application", with "no warranty level or battery life expectancy expressed or implied by these ratings". Its counter-staff guidance goes further. If a customer drives in extreme weather, or runs a vehicle with many electrical options, the guide tells the seller to suggest a battery with more cold cranking amps than the listed minimum: more will not harm the vehicle, fewer may fail early. It repeats the point in its maintenance section, where vehicles worked in extremely cold climates are told to carry a battery rated well above the original-equipment recommendation.

Three things push a real vehicle above its printed minimum:

• Cold. Cold robs a battery of cranking power and stiffens the motor oil the starter has to turn, so the battery gives less at the moment the engine asks for more. The guide states the effect and gives no uplift figure, and neither does this calculator: no battery maker or standards body we could find publishes one, so putting a number here would be inventing it.
• Accessories. Winches, inverters, radios, aftermarket lighting and a long idle at the kerb all draw from the same battery that has to crank the engine afterwards.
• Age. A battery gives its full rated CCA when it is new and fully charged, and less every year after that as the plates wear and sulfate. A battery bought at the bare minimum has no margin left by the time it meets a hard frost in its third or fourth winter.

None of that has a printed multiplier, so treat it the way the guide does: as a reason to choose from the upper part of the printed spread rather than the lower. The cheapest margin on the whole job is buying one step up the range while the battery is new.