Battle-Stone

Battle-Stones are items used to upgrade a battle pet to or  quality.

Polished Battle-Stone can be used to upgrade a pet to uncommon quality, while all kinds of Flawless Battle-Stone will upgrade a pet to rare quality. Polished Battle-Stone and the generic Flawless Battle-Stone can be used on any pet, while all other kinds can only be used on a pet of the appropriate type.

Source
Flawless Battle-Stones of all kinds have a small chance to be obtained upon winning a battle against wild pets. Type-specific Battle-Stones also have a small chance to be obtained from the Sack of Pet Supplies awarded from defeating master trainers.

Players can also trade in any 3 of the same family specific Flawless Battle-Stones for a single Marked Flawless Battle-Stone.

Battle-Stones

 * Polished Battle-Stone
 * Flawless Battle-Stone
 * Flawless Aquatic Battle-Stone
 * Flawless Beast Battle-Stone
 * Flawless Critter Battle-Stone
 * Flawless Dragonkin Battle-Stone
 * Flawless Elemental Battle-Stone
 * Flawless Flying Battle-Stone
 * Flawless Humanoid Battle-Stone
 * Flawless Magic Battle-Stone
 * Flawless Mechanical Battle-Stone
 * Flawless Undead Battle-Stone
 * Marked Flawless Battle-Stone