choosing a replacement car battery: group size, CCA and what actually matters

batteries are not interchangeable, and the three numbers on the label are the ones that decide whether the one you buy fits and works.

group size is physical. it sets the case dimensions and which side the terminals are on. a battery of the wrong group either will not sit in the tray or will not reach the cables, and forcing it is how batteries end up loose, which kills them.

cold cranking amps, or CCA, is how much current it can deliver at minus eighteen degrees. in Ontario this is the number that matters. your vehicle has a minimum. more than the minimum is fine and often worth having. less is a January problem waiting to happen.

reserve capacity is how long it can run the vehicle's electrics if the alternator stops. it matters more than it used to, because modern cars draw current even when parked.

flooded, AGM, and which one your car needs

a conventional flooded battery is the cheapest and suits most older vehicles.

an AGM battery costs more and handles deep discharge and heat far better. if your vehicle has automatic stop-start, it almost certainly requires AGM, because a flooded battery will not survive the number of restarts. fitting a flooded battery to a stop-start car is a common and expensive mistake.

some vehicles also need the new battery registered to the charging system after fitting. skip that and the car keeps charging as though the old battery is still in there, and the new one dies early.

what we do

we fit NAPA batteries and we check the charging system while the vehicle is here, because a battery that failed early usually had help. if the alternator is overcharging, the new battery will go the same way as the old one, and you would rather know now.