Tesla Inc. (TSLA - Get Report) said Monday it will buy Maxwell Technologies Inc.  (MXWL - Get Report) , a battery technology firm based in San Diego, for around $218 million.

Tesla will pay $4.75 for each Maxwell share, the company said, a 54.7% premium to its closing price Friday of $3.07, and bring the company into the corporate fold as a wholly owned subsidiary. 

"We are very excited with today's announcement that Tesla has agreed to acquire Maxwell. Tesla is a well-respected and world-class innovator that shares a common goal of building a more sustainable future," said Maxwell CEO Franz Fink. "We believe this transaction is in the best interests of Maxwell stockholders and offers investors the opportunity to participate in Tesla's mission of accelerating the advent of sustainable transport and energy."

Tesla shares were up 0.22% on Monday. Maxwell rose 49.1% to $4.59.

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