CCA — Cold Cranking Amps
The current the battery can deliver for 30 seconds at −18 °C while staying above 7.2 V. High CCA = strong cold-start performance. The OEM-specified minimum is what your engine needs to crank; anything above that is headroom for the coldest mornings. Higher CCA generally costs more weight (heavier plates, more material) and slightly higher price.
RC — Reserve Capacity
The number of minutes the battery can deliver 25 A at 27 °C while staying above 10.5 V — i.e., how long it can power your accessories with the engine off before the lights dim. RC matters most for vehicles where the battery does work beyond starting: marine deep-cycle, RV house batteries, work trucks with inverters running tools, and modern start-stop cars whose accessories run off battery whenever the engine cuts.
The trade-off
Inside a fixed case size, there's a trade-off between thick high-CCA plates and thinner deep-cycle plates that give better RC. A battery optimised for cold cranking gets less RC; one optimised for reserve gets less CCA. AGM construction loosens the trade-off (the absorbent-mat design tolerates deeper cycling without plate shedding), which is why AGM specs often look strong on both numbers compared to flooded at the same price.
Practical reading
- Daily driver in mild climate: CCA at OEM minimum is fine, RC > 90 min is plenty.
- Daily driver in cold climate: CCA 15-20 % over OEM, RC > 100 min.
- Start-stop vehicle: AGM only, RC > 120 min, CCA at OEM (start-stop cranks gently).
- Marine / RV: AGM or flooded deep-cycle, RC > 150 min, CCA secondary.