According to Official Guinness Records,
The largest collection of Batman memorabilia belongs to Brad Ladner (USA) and consists of 8,226 different items, as verified in Roswell, Georgia, USA, on 11 April 2015.Brad started collecting in 1988, when the 'Batman: A Death in the Family' hit the shelves.
For a complete list of 2015 records, please visit 2015 Guinness Records in United States.