Watch out Energizer Bunny. Robot Evolta kept climbing and climbing _ up a rope dangling from a Grand Canyon cliff for nearly seven hours on a pair of AA batteries that Japan’s Panasonic is billing as the world’s longest lasting.

To prove how durable its new alkaline batteries are, Panasonic had the 5-ounce, 6.7-inch blue imp clasp a rope with its arms and feet and climb as far and long as it could. That turned out to be some 1,740 feet over the course of six hours and 46 minutes, Panasonic, also known as Matsushita Electric Industrial Co., said Tuesday.

The company says the new battery cell _ called Evolta, combining “evolution” and “voltage” _ can keep gadgets running 20 percent longer than offerings from rivals Duracell and Energizer.

Evolta - $5.40 for four in Japan, about 15 percent higher than other AA batteries _ went on sale in April in Japan, with overseas sales planned later this year. The robot was designed by robotics scientist Tomotaka Takahashi.

Guinness World Records certified Evolta as “the longest-lasting AA alkaline battery cell,” based on testing under guidelines set by the industry’s International Electrotechnical Commission this year.