A trio of small Japanese robots will be working together in the Ironman triathlon race in Hawaii next month in a show of their inner strength -- rechargeable batteries. Consumer electronics maker Panasonic will use one set of three rechargeable batteries for the whole 2.4-mile (3.8-kilometre) swim, 112-mile bike ride and 26.2-mile run to power the humanoid "Evolta" robots made by creator Tomotaka Takahashi. Panasonic hopes to reach the finish line in one week, or 168 hours, by recharging the set of batteries shared by the three robots as many times as necessary during the race. The Hawaii triathlon will be the latest in a series of similar endurance campaigns to show off the strength of the Evolta line of batteries. In the past, the company sent different Evolta robots to scale the Grand Canyon, to ride a tiny tricycle in the Le Mans 24 hour race, and to walk 500 kilometres from Tokyo to the ancient city of Kyoto in western Japan. The Ironman cycling and running robots are 23 and 25 centimetres (10 inches) high while the swimming one is 51 centimetres long.