Private equity firm GTCR is purchasing EaglePicher Technologies, a battery and advanced power management system manufacturer, from funds managed by Apollo Global Management LLC. Financial terms of the deal were not disclosed.

Founded in 1843, EaglePicher develops power and battery systems used by customers in the defense, aerospace and medical industries. The St. Louis, Missouri-based target develops battery systems that power a number of key platforms for the U.S. Department of Defense. EaglePicher also touts the U.S. space program as a customer, previously providing the program’s emergency power that successfully brought home the Apollo 13 crew, according to the buyer. The transaction is expected to close in the first quarter of 2018.

GTCR is a middle-market private equity firm based in Chicago. The firm has invested more than $15 billion in capital over 200 companies across the financial services, technology, healthcare and technology, media and telecommunications industries. GTCR’s investments is underlined by the Leaders Strategy, a program that involves “finding and partnering with management leaders in core domains to identify, acquire and build market-leading companies through transformational acquisitions and organic growth.” PricewaterhouseCoopers is acting as financial adviser to GTCR, while Kirkland & Ellis LLP is serving as legal counsel.

GTCR has been active across the middle market. The PE firm acquired GreatCall Inc., an emergency response services provider, for $260 million in 2017. In May, the firm also bought Vivid Seats LLC, a digital hub for users to buy and sell tickets to sports and entertainment events. In April, GTCR acquired medical device maker Regatta Medical Holdings LLC after forming a new trading technology company called Dash Financial Technologies. GTCR won Mergers & Acquisitions’ 2013 M&A Mid-Market Private Equity Firm of the Year award.