Premature shutdown/sleep of MacBook, MacBook Pros (separate from sudden shutdown issue)

On numerous occasions we've discussed an issue where various Mac portables shutdown or go to sleep due to lack of power when the battery status indicator still shows a remaining charge (note that is a completely separate issue from the MacBook sudden shutdown fiasco).

In most cases, this issue is the result of battery indicator miscalculation. The status indicator shows a remaining charge, but the actual remaining charge is significantly lower (or non-extant), forcing the system into sleep or shutdown.

MacFixIt reader Bryan describes his case of the issue:

"Have you heard of any reports of MacBooks shutting down when the battery gets low (30 minutes left or so) instead of warning the user and going to sleep. My Macbook has started doing this (after the firmware update and 10.4.8).  I've called Applecare and they didn't seem too concerned with it.  Of course, they weren't the ones working on a presentation when their computer shut off."

While we're not yet if this issue is more prevalent among MacBooks than other Apple portables, there are a few workarounds that can sometimes prevent the premature shutdown/sleep:

• Calibrating the battery Knowledge Base article #86284 explains the MacBook/MacBook Pro/PowerBook/iBook re-calibration process, which may work to correct this problem in some instances. The document states "The Lithium Ion battery of an iBook or PowerBook computer has an internal microprocessor that provides an estimate of the amount of energy in the battery during charging and discharging. The battery needs to be re-calibrated from time to time to keep the on screen battery time and percent display accurate. You should perform this procedure when you first use your computer and then every few months thereafter." 
• Resetting the PMU.SMU Some users have reported that resetting their portables' PMU or SMU (depending on model) solved this issue. Apple provides details for performing the reset procedure for a number of portable models in Knowledge Base articles #14449 (for PowerBooks, iBooks
and #303319 (for MacBooks, MacBook Pros).
• Using "SlimBatteryMonitor" One solution that has proved successful for some readers is the usage of a third-party battery monitoring utility, such as SlimBatteryMonitor.
• Do not allow battery to fully charge Some users have found that never allowing their batteries to fully charge (disconnecting the power adatper at 98 or 99% charge) inexplicably resolves this issue.
• Using a power adapter In-house, the method we most often use for solving this problem is the simple connection of a power adapter. Doing so usually allows the PowerBook to wake up properly (restoring interrupted open projects) and usually allows several more minutes of charge time even if temporarily connected to the external power source.

Feedback? Late-breakers@macfixit.com.

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