Apple is exaggerating the maximum battery life of its iPhones, according to a new report by Which?, an advocacy group based in the United Kingdom.

Which? said that in tests of nine iPhone models, it discovered that all of them fell short of Apple’s battery life claims by between 18% to 51%.

The worst offender of the bunch was the iPhone XR, for which Apple claimed talk time on full charge that would last 25 hours. Which?’s tests, however, found that the smartphone’s battery only lasted for 16 hours and 32 minutes, for a discrepancy of 51%.

The results for the iPhone XR are surprising, given that battery life was considered to be one of the strengths of the device in its review by Digital Trends mobile editor Julian Chokkattu. The smartphone also provided great performance and a solid camera for its low price tag, compared to the iPhone XS and iPhone XS Max.

“We rigorously test our products and stand behind our battery life claims,” Apple told Business Insider, in response to Which?’s report. “With tight integration between hardware and software, iPhone is engineered to intelligently manage power usage to maximize battery life.”

Which? also found discrepancies with the battery life claims of HTC, though not as much as the differences with Apple’s estimates. HTC’s average talk time for certain smartphones was 20.5 hours, but tests lasted for only an average of 19.6 hours, for a 5% difference.

On the other end of the spectrum, Which? found that Nokia, Samsung, and Sony underestimated the average talk time for their smartphones. Sony smartphones, in particular, were tested to reach 16 hours of talk time, which was 21% higher than the estimated 12.6 hours.

Which? gave Sony’s Xperia Z5 Compact as the opposite example for the iPhone XR. Sony claimed that the model would only last 17 hours, but the advocacy group discovered that it lasts 25 hours and 52 minutes, for almost 9 extra hours.

To conduct its tests, Which? charged up brand new units of the smartphones to full battery, then measured how long they last when making continuous calls. The group also tested to see how long the devices last during non-stop internet browsing.

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