The Collaborative International Dictionary of English v.0.48:

Energizer \En"er*gi`zer\, n.
   One who, or that which, gives energy, or acts in producing an
   effect.
   [1913 Webster]

WordNet (r) 3.0 (2006):

energizer
    n 1: someone who imparts energy and vitality and spirit to other
         people [syn: energizer, energiser, vitalizer,
         vitaliser, animator]
    2: a device that supplies electrical energy [syn: energizer,
       energiser]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "energizer":
   abettor, activator, actuator, animator, arouser, cajoler, coax,
   coaxer, encourager, firer, gadfly, galvanizer, human dynamo,
   impeller, inducer, inspirer, life, motivating force, motive power,
   mover, moving spirit, persuader, pleader, prime mover, prompter,
   restorative, spark, spark plug, sparker, stimulant, stimulator,
   stimulus, tempter, tonic, wheedler