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]