The capacity of a battery is indicated in Ampere-hours (Ah). For instance, 200Ah, 80 Ah, etc. The rate at which the battery can be discharged is indicated by the C rating.
Batteries are usually rated as C/10, c/8, etc. a battery with a 200 Ah capacity and a C/10 rating indicates that the battery can supply 20 A for 10 hours.
The capacity of a battery varies inversely with the discharge rate. Batteries usually have different discharge rates for a fixed capacity.