The Fusion Pack is the main power source for E-frames, the fusion pack acts as a self-regenerating battery providing power to the exoskeletons.
Civilian fusion packs generate much less power than military ones while the latter are (if intelligently applied) a potentially devastating explosive.
Maggie Weston was able to rig a fusion pack with a timer and use it as a make shift demolition charge to bury a brood of Neo-Raptors. During the intial recon stages in preparation for the invasion of Venus, J.T. Marsh used a series of fusion packs to destroy a Neosapien installation.