"We have been investigating the case for some time and now have the evidence to bring a lawsuit," said Sony Corp. spokeswoman Harumi Asai.

The firm claims it spotted BYD Co. at a consumer electronics exhibition in Japan last September, displaying a range of battery products containing the Sony-patent and distributing pamphlets.

Although there was no evidence BYD had begun selling the items in Japan, Sony felt the fact they had held an exhibition and compiled a catalogue meant there was a high chance this would happen in future, said Asai.

"(The offending patents) are related to the structure of the battery," she explained, adding that the lawsuit would be filed later Tuesday at the Tokyo District Court.

"We want to prohibit marketing acts, including sales, in Japan," said Asai.

Sony was not planning to ask for monetary damages.

Asai said the consumer electronics leader put much energy into protecting its intellectual property, with a special team dedicated to investigating possible patent or copyright infringements.

Sony decided to take action against BYD because the patents were used in major batteries that power many of its products, said the spokeswoman.

BYD was not immediately available for comment.

SPACE.WIRE