Depending on the card and associated game, the e-cards are typically used in a key-like function to unlock secret items, levels, or play mini-games when swiped through the reader.

Two versions were released in Japan: the original e-Reader (without a link cable port), which could read cards to unlock game content, etc.

In 2004, Nintendo's head European PR confirmed that the e-Reader would not be releasing in Europe, following a year of confusion surrounding the subject.

This function does not work with the Nintendo DS due to the lack of link cable support.

Data is encoded on the cards using "dot code", a specialized barcode technology licensed from Olympus Corporation.

Smaller games may require scanning only one card (two sets of dot code), while the greater NES games can require as many as five cards (nine to ten sets of dot code) in order to start the application.

When scanned, the e-Reader displayed a Pokédex data entry for the Pokémon shown on the card.

Many of the cards published by Wizards of the Coast included a left side dot code that would allow users to play mini-games, animations, and use secret attacks in the Trading Card Game or play with various songs and graphics.

Once installed, the link cable connector on the Game Boy Advance is obstructed, but a pass-through connection on the e-Reader allows link-up features to be used.

An additional cover (AGB-016) can be added to the e-reader in order to avoid damaging the 6 pin connector when linked to a GBA SP.

The e-Reader fits into the Game Boy Micro and has a link cable port, but not a standard connector.

There were additional Battle-e card sets for Pokémon FireRed, LeafGreen and Emerald in Japan.

Five additional cards were released for a very short time and were packed in with the game and sold exclusively at Walmart stores in the US.

These five cards have become extremely hard to find, as the e-Reader had been discontinued in North America not long after the release of the game.

As for the Mega Man Zero 3 Cards, they change the Resistance Base and add an overhaul of new things to it as well as Weapon Upgrades and Bullet Appearances to make an actual Buster Shot look like a real bullet that an actual gun fires.