Korea's three major electric-car battery makers are losing ground to their Chinese rivals such as BYD and CATL. Their combined share of the global EV battery market fell about nine percentage points on-year from January to May.According to SNE Research on Sunday, LG Energy Solution, Samsung SDI and SK On accounted for a combined 25.6 percent share of the global market in the first five months of this year, down 9.1 percentage points from last year.The biggest, LG Energy Solution, retained its No. 2 spot with a 14.4 percent share. SK On came fifth and Samsung SDI sixth. But CATL and BYD ranked first and third.Korean battery makers' global sales grew from last year, with LG Energy Solution selling 22.6 gigawatt-hours of batteries in the first five months, up 7.9 percent on-year. SK On sold 10.8 GWh of batteries, more than doubling from 4.7 GWh, and Samsung SDI 6.9 GWh, up from 5.2 GWh.But their market share dropped because Chinese companies are growing so rapidly. CATL's EV battery sales more than doubled from 25.1 GWh a year ago to 53.5 GWh, and BYD's sales grew from 6.1 GWh to 19 GWh.