A Pokémon holding this item gains 4 Special Defense EVs whenever it gains experience in battle (EVs are awarded for each Pokémon knocked out in Horde Battles despite experience being gained all at once); its effect is doubled by Pokérus. (In Generation IV, level 100 Pokémon cannot gain EVs in battle; from Generation V onward, they gain EVs whenever they would earn experience.)
The Speed stat of the Pokémon holding this item is halved in battle.
Generation VII onwards
A Pokémon holding this item now gains 8 Special Defense EVs instead of 4 whenever it gains experience during battle.
Outside of battle
From Pokémon HeartGold and SoulSilver onward, if this item is held by a parent when breeding at Pokémon Day Care or a Pokémon Nursery, the Special Defense IV of a parent holding a Power Band will always be passed down to the child. If both parents hold a Power Band, one parent will be selected at random to pass down its Special Defense IV.
||A Pokémon hold item that promotes Sp. Def gain on leveling, but reduces the Speed stat.
|A Pokémon held item that promotes Sp. Def gain on leveling, but reduces the Speed stat.
|An item to be held by a Pokémon. It reduces Speed but allows the holder's Sp. Def stat to grow more after battling.
||An item to be held by a Pokémon. Holding this band reduces a Pokémon's Speed in battle but allows its Sp. Def stat to grow more quickly.