A Booster Shield has a chance of spawning this Booster in Borderlands 2

A Booster Shield is a new type of shield in Borderlands 2

When you take damage, there is a chance that the Booster Shield will spit out a little Booster, and if you go and grab that booster it will instantly recharge your shield. Anyone in your party can pick the Booster up.

Example Booster Shield: Brigworthy Booster Shield