Every robot has its limit.

For the famous Roomba vacuum, it's two to three hours. For the several thousand robots deployed in Iraq, about the same. For the warehouse robots sorting our sneaker orders, eight hours. And the Energizer Bunny? Forget about it -- a few minutes, tops.

Perhaps more than any other factor, the life span of batteries has limited the infiltration of robotics into daily life. As computer processing and sensors have become cheaper and more powerful by the year, batteries, woefully inefficient and slow to recharge, have slogged behind, leaving engineers to dream of a day when they'll have the juice to give life to their boldest creations.

And so roboticists have watched the huge increase in investment into battery technology this year, driven by the new administration in Washington and the push for electric cars, with much interest. This month alone, the Energy Department announced $2.4 billion in battery-related funding.

While the majority of this funding will manifest first in the garage, it will likely allow robotics to push into entirely new, mobile realms, according to Henrik Christensen, the director of the Center for Robotics and Intelligent Machines at the Georgia Institute of Technology.

"We are going to piggyback on whatever they're going to do," he said. "We're never going to be big enough to drive the market alone.

"There is no doubt that new development in robot technology is very much going to benefit from battery technology," he added.

Indeed, for engineers designing robots that operate not tethered to electrical outlets, the field is in a bit of a rut, said Dennis Hong, director of the Robotics and Mechanisms Lab at Virginia Tech.

"We're currently at a design threshold right now," Hong said. "We can't add more batteries, then it becomes heavier. But if it's lighter, [the robot] lasts only 10 minutes."

Perhaps the greatest implication of improved batteries will be in autonomous robots -- machines that not only operate independently but are also able to make judgments and, in effect, think and learn. For purists, these are the only proper robots. The mechanical arms that have long been a mainstay of manufacturing are merely complex tools in comparison.

For decades, most robotics have remained partitioned behind virtual or actual fences, mostly out of the fear that they could accidentally trample or harm humans. Given incipient awareness and long-lasting batteries, robots could now break these barriers, mingling with humans at the job, on the road and in the home.

Such robots are closer than we think, Hong said. At his lab, they have already designed prototype cars that drive themselves, and work is under way on a small, humanoid robot that will give tours of the school campus.

"The technology will be ready before society is ready," he said.

Some autonomous robots are already in use today as factories and warehouses have begun employing the machines to move materials with little human guidance. Christensen's lab is collaborating with Boeing on robots to move its cumbersome, heavy aircraft pieces. And a high-tech start-up, Kiva Systems, has designed an entirely different take on the modern warehouse that uses self-coordinating robots as "movable shelves."

Kiva's robots run low on charge after eight hours, after which they automatically return to charging stations. Longer lasting batteries would allow their warehouse systems -- which have been adopted by high-profile clients like Zappos, an online retailer -- to use fewer robots, lowering costs, said Mitch Rosenberg, Kiva's spokesman.

"Our ideal batteries would cost similar to lead acid, charge as quickly as ultracapacitors and last as long as possible," he said.

Shooting for the moon -- or a better vacuum

Such ideal batteries are a long way off, but that hasn't stopped researchers today from pushing the limits of battery storage. The U.S. military is interested in autonomous robots that can operate for 10 hours on batteries, and NASA's space missions would hugely benefit from longer-lasting batteries, said Allen Sirota, the supervisor of the robotic hardware group at NASA's Jet Propulsion Lab.

The lab developed the robotic rovers, named Spirit and Opportunity, that are currently roaming around the surface of Mars -- years past when NASA expected them to fail. While rigged with solar panels, the rovers remain dependent on batteries, as the meager solar energy they receive needs to be gathered for energy-intensive operations.

"It's kind of like making deposits in the battery bank," Sirota said.

His team is also developing a large, six-legged robot to be used on the moon, if NASA does indeed return there. The energy demands of legged robots is especially high compared with their wheeled peers. But while wheels are efficient in their energy use, they are limited to hard, smooth surfaces like roads. When obstacles come into play -- say, a field of mines or the craggy lunar surface -- then "legs are really king," Hong added.

The current breed of mobile robots is limited also in their strength. The Roomba is a perfect example of this, Christensen said. Its actual vacuum is underpowered compared with plugged-in robots, simply because it cannot spare the charge. Improved batteries will bring truly mobile vacuums and lawnmowers, able to do substantial work for extended periods.

Power problems become even more severe as robots scale down in size. As Mel Siegel, a roboticist at Carnegie Mellon points out, even the Energizer Bunny runs for only three or four minutes before its batteries give out (according to the creator of the animatronic). At microscopic levels batteries, no matter how good, won't be the solution. Energy will instead have to be extracted from the environment, he said, the way microbes do.

In the coming years, people are most likely to begin directly interacting with mobile, autonomous robots in more familiar settings, like the hospital and road. Health care in particular is pushing the industry forward with robot-assisted surgery, which is used in delicate operations on the heart, brain and prostate, for example. In the United States, some 200,000 robot-assisted surgeries were conducted last year, Christensen said.

While many of these medical robots served as extensions of surgeons, robots are now being developed that can conduct surgery on their own and learn from previous operations. Trials on a system that will use a robot to decide the best route for an operation are set to begin next year in Europe, according to a recent report from the U.K.'s Royal Society of Engineering.

And in the home, mobile robotics systems that monitor the elderly and infirm are being developed that will learn from their subjects' typical habits to flag odd behavior such as too much time spent in the bathroom, or not enough eating. Much research is being conducted on designing systems that convey emotions, and already in Japan robots serve as babysitters in shopping centers.

People talk to their cats, and soon, they will be talking to their robots, said Chris Elliott, a contributor to the Royal Society report.

As a society, we have done very little work in conceiving the ethical, moral and legal implications of autonomous robots, Elliott said. In the case of a robotic surgeon that has learned from its previous 50 operations, "What happens in the 51st case when it kills someone?" he said. Can a business be held liable for a machine that learns? And what if the success rate remains higher for the robot than human surgeon? Will we allow robots to make mistakes?

Most scientists working in robotics have long mulled the ethical implications -- today's roboticist is yesterday's avid reader of Isaac Asimov. But they cannot alone determine how the technology they develop will then be accepted, they say. It is a question that will loom for everyone in the future, Elliott said.

There is a simple question to consider, and it may come sooner than any of us expects, he added: "Are we actually going to see a computer in court as a defendant?"

Reprinted from Greenwire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500