INUTEQ water vest. No battery required, just pour 500ml of water from the inlet to use. Purchased on this site and tried on at home. Used only for about an hour outdoors, according to the instructions. INUTEQ cool vest, size L, provides immediate cooling effect using water. - Brand: INUTEQ - Size: L - Cooling Method: Water cooling - Design Features: Mesh material and ventilation holes - Application: Heatstroke prevention Thank you for viewing.