If it is a 15 ft ferret collar then the 393 (AG5) battery should have fitted, as it doesn't then I suspect you have a terrier collar which will require a 357 (AG13, LR44) battery.
As a quick guide 8ft collars take one battery and 15ft collars two batteries. All mk1 collars require either 393 or 357 batteries.
tried the 393s they were way too small for it.im gonna try the other ones you said cheers for all your help good luck