In brief: A new report claims that Apple is exaggerating the battery life of its iPhones. In some cases, the discrepancy between what the company claims and the actual talk time is over 50 percent.

UK consumer watchdog Which? carried out battery life tests on nine different models of iPhones. The results showed that every one missed Apple’s claimed talk times by between 18 percent and 51 percent, with the worst offender being the iPhone XR.

Apple says the iPhone XR will offer 25 hours of talk time on a full charge. But while the handset’s battery life was one of the many elements to receive praise from reviewers, Which? found it lasted 16 hours and 23 minutes—missing Apple’s claim by 51 percent.

Responding to the report, Apple told Business Insider: "We rigorously test our products and stand behind our battery life claims. With tight integration between hardware and software, iPhone is engineered to intelligently manage power usage to maximize battery life.”

HTC is another firm that looks to be inflating its talk time figures, but only by a small percent. Its average talk time for certain phones was 20.5 hours, but Which? found it to be 19.6 hours—a five percent difference.

Some companies’ products performed better in the tests than their official figures. Samsung, Sony, and Nokia all underestimate the average talk time of their handsets. Sony was the furthest off the mark; its phones reached an average of 16 hours of talk time, 21 percent more than the estimated 12.6 hours. Its Xperia Z5 Compact was singled out for praise—the phone’s 25 hours and 25 minutes of talk time is almost nine hours more than the 17 hours Sony promises.

Which? says it fully charged the phones and measured how long they lasted while making continuous calls. It didn’t reveal other details, such as screen brightness, app use, cell coverage, or any background processes that might have been running.