BERLIN—BMW won’t scale up its own battery cell production for electric cars until the technology has developed further, the German company said on Thursday, taking a more cautious approach than some rivals despite record brand sales in 2021. The automaker, which was also upbeat about hitting the top end of its 9.5 percent–10.5 percent profit margin estimate for 2021, currently buys battery cells from CATL, Samsung, and Northvolt among others, but is building its own pilot plant. “We have secured our needs for the next few years very well with the partners we have,” finance chief Nicolas Peter told Reuters, adding BMW wouldn’t rush to scale up its own cell production. “We are not yet at the point where we can say what technology will accompany us for the next 10–15 years,” he said. “That’s why it’s important to invest a lot of resources with worldwide partners in battery cell …