Over the years, the battery life of iPhones has only gone up despite the addition of new features, faster chips, and powerful new cameras. This is due to a combination of more power-efficient internals and software advancements. But exactly how much of an impact do software updates have on the battery life of your iPhone? To find out, a YouTuber has made an exhaustive battery drain comparison video of six major iOS releases — from iOS 10 to iOS 15.

YouTuber iAppleBytes got six iPhone 6s units along with six new batteries for comparison. After the initial calibration, he ran several benchmarks to determine just how much of a difference iOS versions can have on the battery life of an iPhone. The different iPhone 6s units were running iOS 10.3.3, iOS 11.4.1, iOS 12.4.1, iOS 13.7, iOS 14.7, and iOS 15.3.1.

To drain the battery, the YouTuber simulated a real-world use case running different apps for several hours, including using Safari, Instagram, playing Subway Surfer, recording videos from the front and rear cameras, playing a video on YouTube, and more. Interestingly, the iPhone 6s running iOS 14.7 was the first one to die — its battery lasted for only 4 hours 15 mins. This was followed closely by iOS 15.3.1, with a total runtime of 4 hours 36 mins. Older versions of iOS did notably better in the tested and lasted longer.

Below is the full runtime of all the different iOS versions in the test from lowest to highest:

• iOS 14.7 – 3 hours 15 mins
• iOS 15.3.1 – 4 hours 36 mins
• iOS 12.4.1 – 4 hours 58 mins
• iOS 13.7 – 5 hours 19 mins
• iOS 10.3.3 – 5 hours 34 mins
• iOS 11.4.1 – 5 hours 56 mins

The results are very surprising, especially the gap between iOS 14.7 and iOS 11.4.1. It shows that the additional features in newer iOS releases do have a negative impact on battery life.

The YouTuber ran a Geekbench battery drain test on the same set of devices running different iOS releases for further confirmation. This time too, the results were pretty much the same. The iPhone 6s running iOS 14.7 was the first to fully drain its battery, with the units running iOS 12.4.1, iOS 15.3.1, and iOS 11.4.1 following close by.

• iOS 14.7 – 3 hours 4 mins
• iOS 12.4.1 – 4 hours 9 mins
• iOS 15.3.1 – 3 hours 14 mins
• iOS 11.4.1 – 3 hours 16 mins
• iOS 13.7 – 3 hours 22 mins
• iOS 10.3.3 – 3 hours 25 mins

There’s obviously the fact that a newer version of iOS is not as optimized for a chip as the version it launched for. Nonetheless, the results do make it clear that if you want your iPhone to last longer, you should avoid updating to a newer iOS build.