ULSAN, South Korea – To gain economies of scale, BMW is open to sharing with rival automakers the electric vehicle battery cell technology it co-developed with Samsung SDI.

BMW purchasing boss Klaus Draeger said sharing the technology would reduce the cost of the battery cells -- the most expensive part of an electric vehicle.

"If Mercedes called us, we would be happy to find a way with Samsung SDI to supply them with battery cells," he said.

BMW said it plans to increase orders of battery cells from its exclusive supplier Samsung SDI by "at least" 20 to 30 percent in 2016 from its 2014 level.

The supply deal was part of a memorandum of understanding signed between the two companies here on Monday that also included co-development of a next generation of battery cells.

Samsung SDI will increase its supply for the BMW i3 battery powered city car and i8 plug-in hybrid sports coupe and will also supply batteries for future BMW hybrid models starting with the X5 plug-in hybrid, Draeger said.

BMW sold 5,396 i3 cars in the first half globally out of a total of 1.02 million vehicles it sold during the period. The automaker said it raised i3 production to 100 units a day starting in April and will raise output by further 40 percent at the end of summer. The i8 launched in Europe last month and will go on sale in the United States next month.

BMW began working with Samsung SDI, a subsidiary of South Korea's largest conglomerate, Samsung, on lithium-ion battery cells in 2009.

Samsung SDI supplies battery cells to Chrysler in the United States for the 500e battery powered minicar and to Ferrari for the limited edition LaFerrari hybrid model.

For Samsung SDI, which supplies batteries to Apple, the order builds on the company’s plans to expand its automotive business. Its competitors include South Korea’s LG Chem, which supplies Renault, and Panasonic, which supplies batteries to Tesla.

Lee Sang Hyun, an analyst at NH Investment & Securities, said the BMW deal will help SDI have greater presence as an electric car battery maker in the United States and Europe, where it is relatively less well known compared with other battery suppliers.