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Examining the Battery/AC Performance Gap on MacBooks and MacBook Pros

Back in the dark ages, when I used to have a Toshiba laptop, I would always remove the battery when running off of AC power, out of what may have been misguided superstition. I was told, and I fervently believed, that doing so would extend the life of my battery considerably by reducing the total number of cycles. When I got a MacBook, I just stopped the curious practice cold turkey. I didn’t have a reason for it at the time, but it looks like I was right to do so, as users are reporting significant drops in performance on Apple notebooks with the battery removed.

This issue is getting a lot of virtual ink around the blogosphere. Most of the scuttlebutt is actually misleading, too. ZDnet blogs, the Apple Gazette, and TrustedReviews all feature articles that reference the problem as affecting new model MacBooks and MacBook Pros, which is true, but only tells half the story. In fact, the issue is not limited to the aluminum and glass model machines. Gearlog, who ran the tests, doesn’t mention any limit to the models affected, and the Apple Support article officially noting and explaining the issue is actually dated from before the release of the new notebooks, so it must reference previous models as well.

Gearlog’s tests, which put hard numbers on the problem, are indeed conducted with a late-2008 model 2.53Ghz MacBook Pro with 4GB of RAM on board. In their test, which used Cinebench R10 benchmarking software to gather results, processor performance experienced a 37 percent drop running off of AC power with the battery removed, as opposed to with the battery in. A Gearlog reader ran the same test on his white 2.4Ghz Core 2 Duo MacBook and noticed a 50% drop without the battery inserted.

Apple’s official position, according to the support article, is that the processor speed is automatically reduced to prevent the computer from automatically shutting down if it wants more power than the AC adapter provides on its own.

The measure seems designed with the safety of laptop owners’ data in mind, and is probably not a bad thing, in the end. Some commenters, however, feel the move might be an intentional ploy to speed up the rate at which MacBook batteries reach end-of-life, thus requiring replacement. The bottom line is, should you be planning on undertaking processor-intensive activities, best leave the battery in.

What do you think? Do you run your MacBook without the battery? Does this constitute a minor annoyance, a major grievance, or will it have no affect on your computing habits at all? Do you think its possible that Apple is purposely shortening battery lifespans to increase replacement sales?

5 Responses to “Examining the Battery/AC Performance Gap on MacBooks and MacBook Pros”

  1. I went about a year without a battery in my 12″ powerbook, and noticed serious performance issues (DVD player in Leopard wouldn’t run), that were resolved when I replaced the battery.

  2. I noticed this on MacBook Pro 2.2GHz (previous series, non-unibody). I had one bad battery that died after 53 charges and since getting replacementsunder warrantu takes weeks (here in Serbia) I was getting the new one out when I used the laptop for days at home, plugged in.

    I noticed the slowdown with HD trailers from Apple site first. They started to stutter, depending on the bit rate. I looked for answers and found out about this a month ago in Apple Discussions. It’s also siting on Apple’s support site for quite some time:

    Personally, I believe this is annoyance and it should be a option you can witch on/off in the Power preferences.

  3. Funny how ppl forget !
    I remember precisely… This is an issue since the switch to Intel architecture… with the first coreduo, it was said that when removing the battery, the processor would operate at 1 Ghz instead of the 2.16 on my macbookpro 17″.
    So no surprise here and i’m quite astonished so much ppl talk about this !

  4. This is very coincidental. Yesterday I had a row with Apple’s support regarding my MBP battery. Its 15 months old, has 310 cycles and lasts for precisely 38 minutes from a full charge.

    Their response (first line and escalated) was that this was inevitable as I was using the MBP on AC most of the time. They would not replace my battery as, when asked if “it was my fault” the response was “I don’t want to point fingers, but yes. You can buy a new one for £99. What you should be doing was charging to the max, use on battery until charge gets to 50% and then remove the battery”.

    In essence, I can get the full performance and reduced battery life or half-baked performance, good battery life and the risk of losing everything if I yank the AC.

    Not happy. Will now call support again.