The Motorola DEFY MINI is also called Motorola XT320. It uses HF5X battery. In fact this battery is compatible with BF5X which is used by Motorola Defy.

Motorola DEFY MINI Battery Specs.
Part Number: ML-M067
Type: Li-Ion
Capacity: 1700mAh
Replace Code: HF5X, BF5X
Compatible with Motorola Motorola ELECTRIFY, Bravo MB520, Defy MB525, Droid 3 XT862,Photon 4G MB855, Milestone 3 XT883, Motorola Defy Mini, Motorola XT320