The AH of a car battery is a unit of measure which states how long the battery can power a certain load and still retain a usable charge for car starting. The higher the number, the better, and more expensive the battery. ¬†However, this does not mean that you should use the highest AH battery available. This is because every car is engineered to support car batteries of a certain AH. If you attempt to go above or beyond the AH recommended, you may harm your car’s electrical system by either shorting the electrical system or putting a strain on the electrical equipment