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Apple says it was a bug that caused Consumer Reports’ MacBook Pros’ erratic battery life

By Alvin Soon - on 11 Jan 2017, 11:47am

Apple says it was a bug that caused Consumer Reports’ MacBook Pros’ erratic battery life

Last month, Consumer Reports declined to recommend Apple’s MacBook Pros for the first time, due to highly inconsistent battery life results.

For example, in a series of three consecutive battery tests by CR, the 13” MBP with Touch Bar ran for 16 hours in the first trial, 12.75 hours in the second, and just 3.75 hours in the third.

Apple took CR’s claims seriously, with senior vice president of worldwide marketing Phil Schiller tweeting that Apple would work with CR to understand their battery test results. Apple has now issued an official response:

We appreciate the opportunity to work with Consumer Reports over the holidays to understand their battery test results. We learned that when testing battery life on Mac notebooks, Consumer Reports uses a hidden Safari setting for developing web sites which turns off the browser cache. This is not a setting used by customers and does not reflect real-world usage. Their use of this developer setting also triggered an obscure and intermittent bug reloading icons which created inconsistent results in their lab. After we asked Consumer Reports to run the same test using normal user settings, they told us their MacBook Pro systems consistently delivered the expected battery life. We have also fixed the bug uncovered in this test. This is the best pro notebook we’ve ever made, we respect Consumer Reports and we’re glad they decided to revisit their findings on the MacBook Pro.

In a nutshell, Apple says that turning off a setting in Safari not normally used by users triggered a bug that created the inconsistent battery results. The bug has been fixed in the latest macOS Sierra beta issued yesterday, so it may take a while to come to users’ Macs.

However, while turning off the browser cache isn’t common for everyday users, it isn’t an unusual setting to use for a test. By turning off the browser cache, the test forces Safari to download data even when visiting the same page, instead of reading it from the stored cache. That simulates users loading new and different pages, which is what most people do when using their laptops.

There may be more to this story than a Safari bug. A recent poll by 9to5Mac of its readers also found mixed experiences of the 2016 MacBook Pro’s battery life. A full third of the respondents saw half of Apple’s claimed battery life, at five hours or less. A quarter reported six to seven hours, while 15% reported eight to nine hours, and only 6.7% of those surveyed reported the full ten hours.

Our own demanding battery life test of the 13” 2016 MacBook Pro with Touch Bar had its battery life pegged at nearly four hours, while the 15” model managed just shy of three hours. The 2016 MBPs sport a new, slimmer chassis with a correspondingly smaller battery, especially when it comes to the MBPs with Touch Bar (the 13” model without Touch Bar has more space for a slightly larger battery). The 13” MBP with Touch Bar has 34% less battery capacity, while the 15” MBP has 24% less battery capacity.

Consumer Reports says that with the bug fixed, it’s now re-testing the MacBook Pros.

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