Acker, 44, co-founded the subsidiary of Mechanical Technology Inc. (Nasdaq: MKTY) in 2001. He said he would stay on as CEO until the company finds his successor. A nationwide search is underway.

Acker, who previously served as Mechanical Technology president, will remain as an adviser and board member, as well as chairman of the board's technology committee.

He will continue to receive his base salary of $250,000 a year.

MTI Micro makes small fuel-cell systems called power packs that provide power for small electronic devices such as PDAs and cell phones.

He said it was time to bring in a more experienced person.

"We're ready to enter the next phase of growth," he said. "The skills we need in a leader to carry us through the next phase are somewhat different. My love, my passion, my expertise is in the early phase. We have an opportunity to bring in a talented new leader that will carry us forward in this next phase of growth."

Steve Fischer, Mechanical Technology CEO, said Acker's decision was bittersweet.

"Together we just came to the conclusion that in going forward we wanted to look toward a CEO with experience in manufacturing and in penetrating the markets that we're serving--the military, industrial and consumer markets," he said.

MTI Micro's technology is protected by more than 75 patents and applications representing a number of breakthrough discoveries.

The company recently said its technology, called Mobion, had two times the energy of one of the most frequently used military battery.

The successful test comes as the MTI Micro announced plans to enter the government and military market in 2006.

In September, Alan Soucy, MTI Micro's president and chief operating officer, resigned from his position. Acker had assumed Soucy's responsibilities at the time.

The new hire will assume the role of president as well as CEO.