Cranking or Starting battery, this simply means the battery has capacity when correctly sized to start an engine. A larger engine requires a larger battery and the extra volume within the battery gives more surface area for the plates to create a larger chemical reaction to produce more current to start your vehicle/engine.
AGM batteries are designed to have a higher energy density and therefore a higher cranking output. Many times a smaller AGM battery can easily start a vehicle that might have typically had a much larger battery in it. Lithium batteries have a higher energy density again and while there are other considerations with a different type of chemistry they are even smaller and much lighter than AGM batteries because they don't contain a heavy metal (lead).
