6 cell laptop battery vs 12c laptop battery, what would be the differences?

so my laptop battery finally went out. im looking around for a new one right now and i see 2 different kinds. one is a 6c battery and its about 40 bucks. then there is a 12c battery for about 70. i was just wondering what the difference between the 2 were. as far as how much the battery can hold what would the difference be