How my iPad crippled my MacBook Pro

A catastrophic failure's surprising cause was my changed use of my personal computer

When I got home one recent evening, I still had some work to do, so I fired up my MacBook Pro after dinner. It was very slow, which is not how the three-year-old laptop usually performs. Our IT department was switching Exchange servers, and it had been restoring all our archived email to our local computers. From there, the archives could then be moved to the new server when the switch occurs. That slowed down all our systems at the office, and I figured that was happening on my home MacBook as well.

What I didn't know is that my iPad had essentially crippled my MacBook, and that slowdown was the first sign of that problem.

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The next day, the slowness persisted, to the point where Photoshop couldn't even save files -- it would time out, either freezing or crashing as a result. Everything else -- Mail, Safari, Chrome, TweetDeck, Keynote, Word -- crawled along. I spent six hours doing all the things that seemed to make sense to troubleshoot the problem. I ran the Disk Utility to see if my drive had failed; it was fine. I booted from an external drive. I tried older versions of OS X on external drives. I tried different versions of Photoshop -- same problem.

Activity Monitor (a utility similar to Windows' Task Manager that Apple includes with OS X) showed that the OS X kernel -- no matter what OS X version I had booted into -- was using 70 to 80 percent of my CPU time, versus the normal 5 to 10 percent. I saw no rogue apps; in fact, app resource usage was normal. I was stumped.

My brain flashed to viruses, which can slow PCs to a crawl. I've been using a Mac as my primary computer since 2008 (thanks to Windows Vista), and I'd never used antimalware software on them. But I remembered what viruses could do to the PCs I had used before then, so I got an antivirus app and ran it. It turned up no viruses.

I finally did a Web search. (No, I don't stop to ask for direction, either.) The Apple forums had several reports from people with the same sudden, persistent slowdowns and excessive kernel usage. The culprit: a failed MacBook battery. I checked the Battery status menu in the OS X menu bar, and it showed a zero charge and the message "Replace Battery Now." Uh-oh. Although OS X helpfully tells you when your keyboard or mouse battery is running low, it doesn't provide that proactive notification when your battery is failing, though a warning appears in the Battery status menu that none of us really checks.

My MacBook Pro is an early-2011 model, so the battery is not user-replaceable. (On older models, replacing the $100 battery is a two-minute operation anyone can do.) I went to the Apple website and made an appointment to bring it in to my local Apple Store the next day. I figured I'd have no MacBook for a day or two in the course of repairs. Fortunately, I got it back within the hour, with a new battery installed, for $129 including labor. My MacBook ran normally again.

The Apple tech, Zack, told me OS X uses the battery even when the MacBook is powered from an electrical outlet to boost the graphics subsystem. As Intel engineers informed me a couple years ago, Apple is a master at squeezing out the most from the standard PC hardware components it uses because it takes full advantage of the control it has by designing the entire system. Intel's Ultrabook effort was in fact an attempt to provide Apple-like optimized integration to PC makers, who weren't making the effort.

The problem with such a highly integrated approach is that when one component fails, everything else is affected. A dead battery on a PC laptop, or even an older MacBook, would not have had such consequences. I know that from both my pre-2008 PCs and my now-retired 2008 MacBook Pro.

My battery died catastrophically -- its storage capacity was 1.7 percent of normal, Zack told me. That's very rare, and when the battery drops that low, the MacBook has to work much harder to do its normal job. When you're running solely on battery power, the Mac automatically adjusts its resource usage in ways that aren't that noticeable unless you're doing intensive operations. When you're plugged in, the MacBook goes full throttle.

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