The two key differences in car battery specifications are series number, which indicates the size and shape of the battery, and cold cranking amps. Cold cranking amps reflect the amount of electrical current the battery can supply at zero degrees Fahrenheit while still maintaining a usable charge.
Higher cold cranking amps are required for heavier cars and those with higher cylinder compression ratios.
Cylinder compression ratios reflect the amount of fluid and gas pressure inside the engine cylinder when the engine turns over.
A third, less significant, specification difference is a battery's reserve energy capacity. Reserve capacity measures how long a battery can be used to power vehicle accessories when the engine is not running and still start the car.
As of 2015, another consideration is technology type. Conventional, lead-acid batteries, used for over 100 years, work for standard vehicles with normal electrical demands. The enhanced flooded battery is good for improving performance and durability when there are high electrical demands on the battery. The Absorbent Glass Material, or AGM, battery is better suited for modern, fuel-efficient vehicles, has greater reliability and lasts longer.
Some premium batteries also specify C20 capacity, indicating how much energy is stored in the battery.