How much is a Game Boy cartridge worth?

Gray Game Boy carts, Color carts, and fakes of the expensive titles. The label and a boot in a real Game Boy are the check. The battery save may be dead.

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Game Boy cartridges are the small gray or color-specific shells for the original Game Boy, Game Boy Color, and, in a different shape, Game Boy Advance. Loose common games are everywhere. A few titles, especially some Pokémon carts, are both genuinely sought and heavily counterfeited. A cart that does not boot, or that boots and will not hold a save because the battery died, is a used cart with that fault. Dead batteries are ordinary. They are also a repair, and a repair is not the same as a tested saving copy.

Fakes of the expensive titles often have the wrong label sheen, the wrong screw, or a board that does not match photos of an original. If you are paying a rare-title price, look at the board or do not pay that price. If you are selling, and you have not looked, say you have not looked. The video-game article in the journal is the wider aisle. This page is the cart in your hand.

What to look for

Label and region
Title, Nintendo seal, and a model code. A Japanese cart, a North American cart, and a European cart can be the same game and different objects, and some will not play on a regional console without hardware that is not the cart. Read the label. Do not assume language from the plastic color alone.
The shell
Cracks, a worn label, marker, and a third-party shell. The plastic color changed by system. A Game Boy Color cart has a different edge from an original gray cart. Use the right system name in the title.
Save battery
Many games save with a coin cell. If the game says the save failed, or the battery is corroded when you open the shell, say so. Replacing a battery is a known repair. Disclose a replaced battery. Some buyers want it. Some want untouched. Both deserve the truth.
Board, on expensive titles
The chips and the “Nintendo” marking on the board are part of how fakes are spotted. Compare with a current, trusted photo reference, not with your memory of a thumbnail. If it does not match, do not sell it as original.

What moves the price

Title and system
Original Game Boy, Color, and Advance are different markets. A common puzzle game and a chased RPG are different markets. Comp the exact title, region, and condition.
Saves
A cart that plays and does not save is worth less to anyone who wants to play a saving game. It may still be worth something as a repair project. Price the fault, do not hide it for three listings and a return.
Fake tax
You do not get to use original comps for a fake, and you should not pay original comps when the seller will not show the board of a title everyone is faking. Walk.
Boxed
Box and manual are a different, much less common object. A loose cart is the default. Do not borrow boxed comps. The complete-in-box note in the journal is the rule.

Where to sell

eBay
Exact title, region, tested notes, and a board photo if the title is one that is faked. Untested is allowed if you say untested. It is not allowed as a synonym for tested.
Local game buyers
Fine for a bag of common carts. Sort the titles first so a better cart is not averaged into a dollar-a-piece offer you did not have to take.
Keep and play
A common cart in a Game Boy you already own is one of the better small thrift buys. The battery may be dead. The game may still be fun on a playthrough that does not need a save.

What a photo can settle

Front and back labels, the edge contacts, and, if you opened it, the board without glare. Worth can read the title. It cannot see a counterfeit chip through a closed shell, and it cannot know if the save battery still holds.

Questions

Is a dead battery a ruined game?
The game can usually still play. The save is what fails. Replacing the cell is a standard repair if you can solder or if you pay someone who can. Disclose the dead battery either way. Do not call the cart fully working.
Why are some Pokémon carts faked?
Because buyers pay enough that a fake is profitable. That is the whole mechanism. The defense is the board and the label, compared carefully, plus a price that is not magically low from a seller who will not show either.
Does the color of the shell tell me the system?
It helps. Original Game Boy carts are gray. Color carts are often translucent or a different shape at the edge. Advance carts are a different, smaller format. Read the label anyway. Third-party shells exist.

From the journal