Tom's Guide has published the results of a battery comparison test pitting Apple's new iPhone XS and iPhone XS Max against a variety of smartphones, with some surprising results.

Both of Apple's latest flagship models failed to reach the heights of last year's first-generation iPhone X using the same battery endurance test, which involved surfing the web continuously over a 4G data connection. Displays were set to 150 nits of brightness, with both auto-brightness and TrueTone disabled.

The iPhone XS Max lasted 10 hours and 38 minutes, while the iPhone XS managed 9 hours and 41 minutes. Those figures compare unfavorably to the results of the original iPhone X, which lasted 10 hours and 49 minutes in the same test last year.

As far as rival phones go, the iPhone XS and XS Max outperformed the HTC U12+ (9 hours, 13 minutes) and the LG G7 ThinQ (8 hours, 35 minutes), however both Apple models were beaten by flagship devices in the Android category. Google's Pixel 2, for example, lasted 12 hours and 9 minutes, while Samsung's Galaxy Note 9 lasted 11 hours and 26 minutes. However, the overall winner was Huawei's P20 Pro, clocking in 14 hours and 13 minutes.

Apple advertises that the iPhone XS can last up to 12 hours during internet use (the same figure given for last year's iPhone X) while the iPhone XS Max can last up to 13 hours on a single charge. However, battery performance can be affected by various factors, including OS version, hardware optimization, and even cellular reception, which is why Apple only offers approximate numbers.

Earlier this week, iFixit teardowns confirmed the existence of a new single-cell L-shaped battery in the iPhone XS, while the iPhone XS Max remains two cells. Chinese regulatory filings also earlier revealed the iPhone XS and iPhone XS Max have battery capacities of 2,658 mAh at 3.81V and 3,174 mAh at 3.80V respectively.

Last year's iPhone X has a battery capacity of 2,716mAh at 3.81 V, yet Apple claims iPhone XS customers can expect a 30-minute increase in operating time over that device, while XS Max users can expect an hour and a half. If you're an iPhone XS or XS Max owner, let us know what kind of battery life you're seeing by using the comments below.