Application cache on Safari has no limit on storing data, but for mobile Safari the rues are different.The upper limit is 5MB.
On mobile safari, the local storage and session storage are 5MB each. On WebSQL, a user is asked for permissions but you cannot store data any more than 50MB.
With the latest iOS version, if a web app needs more then 5MB of cache storage, a user will be asked if it has permission to increase it. This is done so that the user can manage own memory space.