Currently Being ModeratedMay 1, 2013 5:51 AM (in response to tamarfromga)
Reset the SMC > http://support.apple.com/kb/HT3964 If it doesn't work, the next thing you can try is to reinstall Mac OS X, and finally, if it doesn't do anything to solve this problem, take your computer to an Apple Store or reseller to get the battery replaced
Currently Being ModeratedMay 1, 2013 7:12 AM (in response to tamarfromga)
The amount of fluctuation you are seeing is fairly high. Let me explain how the time estimate works and we can go from there. Your Mac knows "about" how long the battery will last. It calculates this based on how hard the machine is working. For example, if it's just sitting there idle, you may see a six hour estimate. If you start running something that uses lots of processing power, it may instantly drop down to three hours. If you use the car analogy... if you're just coasting along at a steady speed, you may get 20 miles to a gallon... however, if you suddenly find yourself climbing a steep hill and you need to really press down on the gas to climb it, your car is going to use a lot more gas... so it will run out faster.
What the time remaining shows is an estimate of how long the battery will last if you leave the system just as it is. As soon as you start running programs and using more power, it adjusts the remaining time accordingly. For example, if you're just reading a plain text web page, you may see 7 hours remaining. Your computer says "Hey, this is easy, I can do this for 7 hours". However, if you decide to start playing videos or games, your computer will say... "Hey, I'm having to work a lot harder now... I this pace, I'm only going to last three hours".
So, depending on what you are doing at any given time, that number can fluctuate greatly. A better way to monitor your battery is to monitor the percentage (just click the battery icon and select "percentage"). This will show you the "actual" percentage remaining. It won't fluctuate like the time remaining estimate.... it will just go down faster under a heavy load and it should never go up (until you start charging it).
The fact that you're getting about 7.5 hours would seem to indicate your battery is working fine.
Currently Being ModeratedMay 1, 2013 7:27 AM (in response to JoeyR)
Just to clarify... the estimated runtime (left on the battery) is reported from the battery NOT calculated by the Mac. In addition the estimage is based on an average use over the last 30 seconds. So the time fluctuates as Joey indicated as your use changes.
This uses Smart Battery System (SBS) commands called Time to Full and Time to Empty.
the math is pretty simple but when you add the run-time fluctuations you can see a wide range of estimated times.
The battery has capacity RC (Remaining Capacity) and an average current IAvg:
Time To Empty is RC / IAvg
so is the average current changes much the time will also change.
you can "watch" this by open the application "System Information" in the Utilities folder, and refreshing while do differnt activities:
As shown in the screenshot... my machine is charging (so the sign of the average current is "+") discharge current is negative
Currently Being ModeratedMay 1, 2013 8:27 AM (in response to mende1)
Thanks so much. I will try what you suggest. I need to say, however, that the reseller's tech claims that he replaced the battery. So I wonder whether you are suggesting that if all troubleshooting attempts fail you suggest that I ask the reseller to replace the replacement?
Currently Being ModeratedMay 1, 2013 8:33 AM (in response to JoeyR)
Thanks for your clear explanations, Joey. I should have added to my original question an important detail: The fluctuations occur even when I intentionally leave my computer "idle" with only Safari and Mail running, and AirPort On. This is what mystifies (and concerns) me. I hope this important detail provides another clue to what might be happening (or not).
Currently Being ModeratedMay 1, 2013 8:36 AM (in response to mende1)
So though the battery took 7.5 hours to run down to zero (despite the crazy fluctuations, and the last five hours I wasn't near the computer), the replacement battery could still be defective, and a cause or the cause of the wild fluctuations?
Currently Being ModeratedMay 1, 2013 8:37 AM (in response to tamarfromga)
What happens with the battery isn't normal. Before taking the Mac to the Apple Store or reseller, try what I told you in my first comment. Then, if nothing works, take it, because the battery could be defective, even if the capacity is correct
Currently Being ModeratedMay 1, 2013 8:46 AM (in response to mende1)
Thank you for confirming my sanity;-( I will try the suggestions in your first comment. I don't recall the last time I reinstalled the OS. Would you give me tips on ways to avoid accidentally messing up my data or doing who- knows-what irreversible no-no? Or point me to a discussion on this board or elsewhere with such explicit instructions? And while I am a seasoned content developer, I get a bit queasy doing things unsupervised such as reinstalling the OS.
Currently Being ModeratedMay 1, 2013 8:48 AM (in response to tamarfromga)
You won't lose anything reinstalling OS X, but just in case, make a backup on an external disk with Time Machine. To reinstall OS X, just insert the Mac OS X DVD, hold the C key while your Mac is starting and follow the on-screen steps to reinstall OS X. After reinstalling, open > Software Update, and install all the available updates