1. a person or thing that gives energy, enthusiasm, or motivation to others
Usage: British spelling; American spelling is 'energizer'
2. a battery or power source that supplies electrical energy
Usage: British spelling; American spelling is 'energizer'; often used in product names

Examples

• The new team captain proved to be an energiser, lifting morale throughout the season.
• Coffee is a natural energiser for many people in the morning.
• She's an energiser in the office—everyone feels more motivated when she's around.
• The energiser in the remote control had run out of power.
• His enthusiasm acts as an energiser for the entire project team.
• We need to replace the energiser in the smoke detector.