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Dear Tom and Ray:

What is the difference between cold cranking amps and hot cranking mps? Which is more important in choosing a battery? Because of health reasons, I just use my car once a week to go shopping in town, so I need a good, strong battery. - AlexanderTOM: Cold cranking amps (CCA) and hot cranking amps (HCA) are two different ways of rating how powerful a battery is.

RAY: And generally speaking, you should look for a battery with the greatest number of CCA you can find. The higher the CCA, the more lead plates a battery has and, therefore, the stronger it is. What that gives you is more cranking time on a cold morning before your battery rolls over and plays dead.

TOM: For you scientists out there, CCA is a measure of how many amperes the battery can put out for 30 seconds at 0 degrees Fahrenheit - while still maintaining enough voltage to start the car.

RAY: If you're looking for a benchmark, Consumer Reports says the best battery is the Interstate Megatron MT-34, with 650 CCA. But we'd say that any battery with 550-600 CCA is above-average.

TOM: HCA is a term that some marketing executives came up with to make their cranking amp numbers higher. By performing the test at a higher temperature (32 degrees Fahrenheit instead of 0), a battery's HCA always comes out about 15 percent higher than its CCA. If you're looking at batteries measured in HCA, look for one with at least 650 HCA.

RAY: Another option you could consider is one of those new "Switch" batteries. Those are batteries that come with small, attached "spare" batteries for emergency starts. They give you something none of the conventional batteries give you: DCA - dead cranking amps. If you leave your lights on and your battery dies, all you do is flip a lever, and the "reserve" battery gets you started.

TOM: But the disadvantage of the Switch battery in very cold weather is that neither of its two batteries is all that powerful. The main battery provides 460 CCA, which is OK, but not great. The reserve battery has only 180 CCA, which can get you started in good conditions, but might not help you when it's bitterly cold out (when your main battery is also most likely to fail).

RAY: If you have a history of leaving your headlights on, or live in a moderate climate, the Switch can give you some peace of mind for about twice the price of a regular battery. But if you simply want the best chance of starting your car at any given time in any climate, our general recommendation is to get the battery with the highest CCA you can find.

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