15 Comments

Summary:

I am still trying to get my head around this article on Gearlog that points out that Apple notebooks throttle the CPU performance if you run them plugged in without a battery installed.  They discovered this "feature" by accident while performing benchmarks with different types of […]

Battery_arms_114466I am still trying to get my head around this article on Gearlog that points out that Apple notebooks throttle the CPU performance if you run them plugged in without a battery installed.  They discovered this "feature" by accident while performing benchmarks with different types of RAM.  They kept seeing different results and then figured out that the benchmarks run on the MacBook Pro while plugged in but without the battery installed consistently clocked in with 37% lower performance.

You may want to read that last sentence again.  If you pull the battery out of your MacBook Pro and run it while plugged into the power outlet your MBP will slow down almost 40%.  This intrigued the Gearlog folks so they went digging and found a discussion on the Apple support document that describes what is going on:

If the battery is removed from a MacBook or MacBook Pro, the computerwill automatically reduce the processor speed. This prevents thecomputer from shutting down if it demands more power than the A/Cadaptor alone can provide.

Say what?  That doesn’t make sense to me as I wouldn’t think that any notebook would be drawing power from both the adapter and the battery at the same time anyway.  Any electrical engineers out there who can explain this?  Do other non-Apple notebooks do this?  Has anybody seen this first-hand?  Inquiring minds want to know. 

  1. Companies decided that a 60 watt power adapter sells better than a larger 120 watt adapter because it can be physically smaller. They also learned that they could get away with lower wattage adapters than a laptop needs at peak performance since they have extra power in the battery. This isn’t an issue since most computers twiddle their thumbs looking for something to do most of their lives allowing the battery to charge.

    So in Apples case, people love their small adapter. So instead of giving people a larger adapter when they gave them a more powerful computer, they just clock it down a bit when there isn’t a battery.

    I had a dell laptop with a bad battery that would shutdown if I pushed it with a 60 watt power adapter. The 90 watt adapter would be able to keep it running.

    Share
  2. Interesting. As Cody B said, it must be because the batt can sumplement the power requirement in high-wattage scenarios.

    Steve.

    Share
  3. I have a pavillion notebook from HP, and if I take the battery out while it is plugged in, performance does not drop. but if I try to do too much then the notebook will sut down claiming a dead battery. mainly the A/C cable is there to charge the battery, but if the computer is eating battery power too fast it will draw from the A/C plug as well

    Share
  4. I have a pavillion notebook from HP, and if I take the battery out while it is plugged in, performance does not drop. but if I try to do too much then the notebook will sut down claiming a dead battery. mainly the A/C cable is there to charge the battery, but if the computer is eating battery power too fast it will draw from the A/C plug as well

    Share
  5. It might help to think of both the battery and the AC supply as both contributing to the power available. The laptop doesn’t switch from battery power to AC power when you’re plugged in, they’re both active.

    Share
  6. Yeah this isn’t new. I remember people complaining about the issue when the Macbooks first came out several years ago. It isn’t specific to Apple either. Thinkpad’s (Lenovo) and Dell’s do the same thing. As mentioned above the battery acts as a UPS of sorts for short transients when performance is maxed out. The battery handles those short power spikes better than the power adapter.

    Share
  7. I guess it is like a hybrid car. The battery kicks in to help the engine in high load situations.

    Share
  8. I have the HP HDX Dragon, unfortunately it does the opposite of the Apple notebook. I get full speed with the AC adapter installed (battery in or out). However once the AC adapter is disconnected, the CPU clocks down and there is no way to speeding the Dragon back to full speed. Maybe its a good thing since on full load with 3D games, the notebook does pull around 120Watts hence the battery may discharge too fast (84Whr capacity).

    Share
  9. John in Norway Friday, November 21, 2008

    This sounds like a copout. My old Fujitsu 3GHz P4 laptop chugs along quite nicely without the battery (which died many years ago). – Looks out the window at the ginormous power brick sitting in his garden melting all the snow.

    Seriously, though, the adaptor is huge and it gets mighty hot (as does the whole laptop!). It outputs 20volts, 6Amps.

    Share
  10. aesthetics over performance, anyone surprised?

    Share

Comments have been disabled for this post