Apple is exaggerating the maximum battery life for several of its iPhones, a new consumer advocacy report concludes.

According to U.K. consumer group Which?, in tests of nine iPhone models, all of them fell short of Apple's battery life claims by between 18 and 51 percent.

The group carried out tests to determine average talk time for a range of models, including the iPhone XR, which had the biggest overestimation for talk time on a full charge. In Which? tests, it lasted for 16 hours and 32 minutes — whereas Apple said it would last 25 hours.

HUBBLE CAPTURES STUNNING SPIRAL GALAXY IMAGE

"With mobile phones now an essential part of everyday life, we should be able to count on our handsets living up to the manufacturer's claims," said Natalie Hitchins, Which? head of home products and services, in a statement.

"There are clearly questions here around how long some mobile phone batteries will last and so it's important to make sure you find an independent source of reliable information when buying your next phone," Hitchins added.

Which?, a consumer advocacy group that tests a wide range of products regularly, is seen as the British version of America's Consumer Reports.

REAL LIFE 'JAWS': TERRIFYING GREAT WHITE SHARK IMAGE MIRRORS 1975 CLASSIC FILM

Apple disputed the results in a statement to 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. Our testing methodology reflects that intelligence. Which? haven't shared their methodology with us so we can't compare their results to ours. We share our methodology for testing which we publish in detail here."

In order to complete its testing, Which? examined over 50 mobile phones from five popular brands. It purchased the phones at full battery strength and timed how long they lasted when making continuous calls. It also ran other tests before making a ruling on battery life.

CLICK HERE FOR THE FOX NEWS APP

Fox News reached out to Apple for comment on the study.