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