I love Nintendo carts because they're damn near indestructable. Twenty five years later and every NES cart I've run into has worked perfectly. Most of the time all they need is a gentle cleaning. Sometimes though you run into dead batteries. That's my biggest worry when buying older NES games. How long is that alreadt 20+ year old battery going to last? That's why I put in new batteries in all my battery backed NES games before I get started playing. I use a CR2032 battery holder that's modded to fit in an NES cart with a brand new name brand battery. Cheap batteries from ebay usually have half a charge or are cheap Chinese knock offs avoid them!