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On the Apple website it says the MacBook Pro 17" has a 8 to 9 hour battery life. I got home from work (having it plugged in at work) at about 7pm and I went to bed at 10pm. In this time I watched a few shows on the Mac and did I bit of browsing.

I take out the Mac this morning and there is only 30minutes of power left. How do you explain this?

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up vote 3 down vote accepted

The claimed battery life is usually specified for a workload that consists mostly of browsing or 'word processing', with the display dimmed to minimum and almost no additional applications running.

Display brightness is one of the biggest consumers of battery power. Video playback taxes the GPU and draws additional power (and if it's Flash video, which is a notorious power drainer, you can expect this to go down even faster) and so do the speakers. All these factors combine to reduce battery life.

The number of cycles and reported battery health also influence what your battery's maximum life can be. Over time, batteries lose the ability to store as much charge as when they were new (this is a limitation of how most rechargeable batteries are designed) and if they are not used regularly (computer unplugged) the health goes down even faster. You can use coconutBattery to see what the state of your battery is. If the health seems to be particularly low, you may check back at the Apple Store to see if you're eligible for a battery replacement.

As a final note, I'm assuming from your question that you own the 17" MBP with the integrated battery for which the 8-9 hr life is claimed; older models have a lower capacity battery that gets around 5 hours depending on workload.

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This shocking! I only bought it 6 months ago. Yes I was watching flash video with speakers over wifi but from 9 hours to a little under 3 hours? That is truely shockingly bad! – TheLearner Nov 16 '10 at 9:12
@user38352 Apple has one of the most honest assessments of real world battery life afaik. But flash video (i.e. Youtube, Hulu, etc.) is draining the battery criminally fast. This is also one of the reasons why Apple rejects Flash for iOS devices. I read somewhere (unfortunately no source available) that Flash can drain a mobile device battery (pad or phone) in under an hour. – Daniel Beck Nov 16 '10 at 12:07

Your usage probably does not match that of the test conditions for their results.

Watching any video will reduce the amount of battery power significantly, and the brightness of the display will count towards this as well. If you were watching a DVD, the moving parts in the ROM will contribute to lower battery life as well.

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To build on @alexandru's and @ Randolph's answers, much of it depends on your individual usage. I have a pre-unibody MPB 15", which I've had for three years. In that time, I've gone through 3 batteries (about one per year); fortunately for me, Apple has replaced the batter twice at no cost to me (other than my Applecare warranty).

After speaking to Apple 'geniuses' a couple of times, and once more two nights ago, you need to fully drain the battery at least once a month (run it from a full charge to 0% (where it turns completely off and goes into hibernation), then charge it back up to 100% without unplugging the power cord. If you can't 'cycle' the battery in that way, as they call it, I was also told to try and keep the battery between 20% and 70% charge at all times. Setting up an event in iCal to remind you is also helpful.

Again, your usage will affect battery life (duration of charge) and watching videos, listening to music, extensive wireless communication (web browsing or transferring files over the network), gaming or anything CPU intensive or spins the hard disc or optical drive often will drain the batter much faster than, say, writing a paper in Word.

If you're experiencing very bad battery life early in the machine's life, take it into an Apple store and explain the problem. In both my cases, the Genius I spoke with replaced the battery for free then gave me tips on how to extend the new battery's life (which I'm passing on here).

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