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I have a white MacBook (MacBook4,1). I have owned and used it for over two years now (30 months, as coconutBattery would have me believe). coconutBattery and Battery Health Monitor both report that the capacity of the battery has gone down to 82% at 4123 mAH charge capacity (with design charge capacity being 5020 mAH). The load cycles (cycle count) is 376, and the battery is reported to be in normal condition.

Naturally, the battery drains faster now than it did, say, a year ago, or when it was brand spanking new. I don't mind that. That's understandable. What I do mind, however, and what perplexes me is that, after the battery is drained all the way down to around 30%, the MacBook shuts off in a split second. I can hear that familiar click sound from the hard-disk that comes when the power button is held down for a few seconds to forcefully shut down the system. It took me by surprise when I first experienced it. I thought that perhaps it went to sleep because the battery may have drained completely. But it never displayed any alert about low battery (the charge was still reported to be around 30% when the event happened). When I pressed the power button, the MacBook did a POST and started as it would after a cold shut-down.

It happened to me every time I had drained the battery down to around 30%. I would think that the electronics on board the battery controller would force the system to go into hibernate (suspend/sleep) mode, while making sure there is just enough charge left to keep the system memory alive somewhere. However, as far as I can tell, obviously, the controller has no reason to think the remaining charge (at 30%) on the battery is appallingly low to warrant any such operations. But, it is as if the battery suddenly abruptly completely shuts itself off, as if its connection gets severed off there in a second.

I am clearly out of any warranty. But, I would like to know what could be the problem here. The battery is dying, but at 82% capacity, I shouldn't think so. What do you people think?

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3 Answers 3

up vote 3 down vote accepted

I had the exact same problem (twice!) and had my battery replaced under warranty - I seem to recall there was a battery replacement program for this issue (don't quote me) but even if there was I suppose that would have finished now.

I'd say you might have a chance if you called and explained the issue or went into an Apple store depending on what kind of person you run in to.

There was also a firmware update that was meant to help solve this issue, but it didn't help me and I suppose you'd have gotten that through software update long ago.

Long story short: It's not that the battery isn't holding enough charge, and not that it's had too many cycles - evidently they just had an issue with their battery production, and your machine has taken this long to be affected by it. Hopefully you get someone nice from Apple, but otherwise a trip to eBay or somewhere else on the internet should be able to get you a new battery for relatively cheap.

Good luck, hope it works out for you.

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Thank you for sharing your insights. Yes, I have all the updates installed on this system. I will check with an Apple Store, though I have a feeling I will have to end up getting a new one. –  ayaz Mar 14 '11 at 11:30
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No early alert and indicating 30% charge when the charge is exhausted suggests the battery needs to be calibrated, assuming you haven't done this recently. See this Apple support page for details, but the gist of it is that measuring a battery's state of charge is inexact, so by calibrating it occasionally, it will reset the software's model of the battery state and discharge characteristics, and give a more accurate measurement of the remaining charge.

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Thanks for your reply. Before I discovered the problem, I used to calibrate the battery once every couple of seconds. Now that the laptop shuts off suddenly at around 30% charge left, I am not sure how to properly perform the calibration process. –  ayaz Mar 14 '11 at 11:29
    
The calibration process I'm talking about involves a complete charge, discharge, and re-charge. I don't see how that would be doable in less than half a day. Are we talking about the same process? –  JRobert Mar 14 '11 at 12:26
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You need a new battery. After many years of usage, chemicals in laptop batteries will be less active and therefore hold less charge. The sensor in the laptop usually detects the voltage of the battery to imply how much percentage of charge it still holds. And the laptop can only function when the battery provides a certain level of power voltage. As batteries age, the original electronic properties of the battery changes also and the sensed voltage change is no longer a good indicator for how full the battery is charged. When the battery voltage drops lower than the minimal required voltage to drive the machine, the computer automatically shuts down to protect its own circuits from being damaged by insufficient power. That's why you will hear a click and then everything shuts down without warning.

So you need a new battery, or just use your laptop with power cord plugged in.

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Thank you for your reply, MacDaemon. –  ayaz Mar 14 '11 at 11:31
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