Cold Cranking Amps (CCA) is a battery rating that measures how much current the battery can deliver at 0°F for 30 seconds while maintaining at least 7.2 volts. Higher CCA means better cold-weather starting performance.
Every vehicle has a manufacturer-specified minimum CCA. It's listed on the door jamb sticker or in the owner's manual. Replacing a 700 CCA battery with a 500 CCA 'equivalent' for $15 less results in marginal cold starts and premature failure.
Going higher than the original CCA rating doesn't harm anything — the alternator only charges what the battery needs. Going lower causes problems.
In cold-weather markets, prioritize CCA over reserve capacity. In hot-weather markets, prioritize reserve capacity over CCA. Most batteries advertise both — pick the one that fits your climate.
Aged batteries lose CCA capacity over time even if they still 'start' the car. A 3-year-old battery rated at 700 CCA may now deliver only 400 CCA — enough for warm weather but not enough for a hard freeze.