Tesla is buying Maxwell Technologies Inc for $218 million in an all-stock deal that will help the electric car maker beef up its battery technology.

Maxwell, based in California, makes ultracapacitors that are used in automobile batteries to lengthen their lives. They are also used for electric energy storage on power grids. Maxwell's customer list include General Motors and Lamborghini.

Ultracapacitors, combined with the energy of batteries, can enable rapid response times, extend operational temperature range and lengthen battery life by up to two times, according to Maxwell.

Maxwell has also recently been talking about a dry electrode technology for batteries. The company claims that its electrode enables an energy density of over 300 Wh/kg in current demonstration cells and they see a path to over 500 Wh/kg.

“We are always looking for potential acquisitions that make sense for the business and support Tesla’s mission to accelerate the world’s transition to sustainable energy,” Tesla said on Monday.

Maxwell expects the deal, which has already been approved by its board, to close in the second quarter of 2019, or shortly thereafter.

Currently, Panasonic is the exclusive battery cell supplier for Tesla cars.