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I have a mid-2009 white MacBook. About a week ago, I switched the aging and failing battery for an identical new battery I got off eBay (supposedly original part and new - looked legit both in description and packaging).

After switching the battery and resetting the SMC, a fully-charged battery reports six hours of available battery life, the way it should. But the battery runs out after only three or so. Pretty much the same battery life I got out of my old battery.

Could there be something I'm doing wrong software-wise here, or is it likely that I got a shitty used battery which was polished and made to appear new?

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up vote 3 down vote accepted

The first step is to look at the detailed battery information from the System Information/System Profiler for each battery.

  Charge Information:
     Charge Remaining (mAh):     5587
     Fully Charged:              Yes
     Charging:                   No
     Full Charge Capacity (mAh): 5611
  Health Information:
     Cycle Count:                289
     Condition:                  Normal
  Battery Installed:          Yes
  Amperage (mA):              0
  Voltage (mV):               12420

Pay attention to the Full Charge Capacity and cycles for each battery.

The second step (assuming my guess that you have a non-unibody Mac where the battery is user-replaceble - swappable without removing the bottom of the Mac) is to run a simple calibration charge cycle on the new battery (and followed by the old one perhaps to compare). Once your computer gets to know the new battery (it guesses based on average battery performance until it determines the chemistry particular to each battery that gets used over time).

The third step if you really want to measure everything on both batteries is to use the pmset -g pslog command to document each battery as it powers your Mac from full to the low power shut off point.

Here is the relevant section from the man page linked above:

 If your system suddenly sleeps on battery power with 20-50% of capacity
 remaining, leave this command running in a Terminal window. When you see
 the problem and later power and wake the computer, you'll be able to
 detect sudden discontinuities (like a jump from 30% to 0%) indicative of
 an aging battery.
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Thanks, this really helps. The only ting I'm unsure about is the calibration cycle charge - according to the link, my computer's battery is "pre-calibrated". Is the calibration procedure for this battery just fully charging it, completely discharging it and leaving the computer off for a few hours? – Geir Smestad Sep 16 '12 at 10:11
Yes - Leave the power connected and the charger for green for two hours. This allows the charge to equalize in all the cells and the trickle charge to top things off. Then put away the power cable. Running for a day or two days until it's out of all power and shuts itself off. Then leave it for 5 hours in sleep so it can go to the second low level and really shut off completely. Even though the battery is calibrated - the computer needs to know how it works and each is different. They change over time, so you may repeat this every 6-14 months if you wish. – bmike Sep 16 '12 at 18:17

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