Bought recently off ebay. Wasn't cheap, had the usual signs inside the cartridge and on the back so it looks like a genuine copy. When I boot the game up, I get a message that says "The internal battery has run dry. The game can be played. However, clock-based events will no longer occur."
My research tells me that anything along the lines of "the game can be played" means it's a fake. However, other sites tell me that there is an exception if the game detects a problem with the internal battery, and the game played message wasn't the last bit of text like it normally would be with a fake copy.
Expert opinions needed.