The Motorola Electrify is actually a renamed version of the Motorola Photon 4G which released by U.S. Cellular. It uses HF5X battery. In fact this battery is compatible with BF5X which is used by Motorola Defy.

Motorola Electrify Battery Specs.
Part Number: ML-M067
Type: Li-Ion
Capacity: 1200mAh
Replace Code: HF5X, BF5X
Compatible with Motorola Motorola ELECTRIFY, Bravo MB520, Defy MB525, Droid 3 XT862,Photon 4G MB855, Milestone 3 XT883