I got a new computer from work: Macbook Pro 2015. Opened it up and the expected battery life read 14 hours.

Used Migration Assistant to upload my old computer, a 2013 Macbook Air. Migration worked fine and the laptop was plugged in the entire time.

Now, a day later, with the laptop on idle and literally zero apps open and the screen on medium brightness and all that, the expected battery life is 4 hours.

How is this possible?

EDIT Added details.


2 Answers 2


If it is relatively clean installation of macOS, then Monomeeth's answer is a good way to rectify the situation with a battery and other hardware and the OS that are not communicating properly anymore. But that way excludes the other possibilities. Therefore I'd like to add a few small bits.

Regarding "How" it's possible:

  1. The "time remaining" is only an estimate. You shouldn't depend on that. Orient yourself on the hard data. Hard data is the electrical data: actual Current Charge and Full Charge Capacity compared to the Design Capacity. When on battery power another reading comes into play: Discharging with… Apple removed the time remaining estimate, because it is only an inaccurate estimate and apparently too confusing or disappointing to users (this is not directed at the OP).

  2. However, a 2015 MBP is not 'new' regarding the battery in 2017. If the battery wasn't replaced in the meantime, then it is also possible that it simply didn't age so well. That might depend on usage or non-usage, being the odd lemon etc. Comparing the specs of the battery with actual readings might give unwelcome surprises there. For a quick glance of battery values use Coconut Battery or any other such tool.

  3. Even more likely: Migration Assistant is not infallible. It might have introduced cruft or incompatible software. When that runs in the background the machine could look idling, with "zero apps open" but is working hard behind the scene. The same effect might occur if all the software brought over with Migration Assistant is trouble free but all the data still has to be indexed by active Spotlight processes. So look into Activity Monitor and Console.app and double check that the computer is really idling.


The 14hrs of battery life the MBP reported initially was almost certainly an incorrect reading.

The first thing I would do is reset the System Management Controller (SMC) and see what readings you get then.

Reset the SMC

  1. Shut down your MBP
  2. Unplug the power cable and any other hardware (keyboards, mouse, drives, etc)
  3. For 10 seconds, press and hold at the same time the shiftcontroloption keys (on the left side of the built-in keyboard) and the power button
  4. After 10 seconds let go of all keys and the power button
  5. Plug in the power cable
  6. Turn your MBP back on with the power button.

Once you've done that see if you notice any wild fluctuations in what the system reports in terms of your battery life.

Run Apple Diagnostics

After resetting the SMC you can also follow the steps below to run Apple Diagnostics if you're still concerned:

  1. Fully shut down your MBP
  2. Restart your MBP
  3. Immediately press the D key and keep it down until you see the Diagnostics screen appear
  4. Wait for Diagnostics to finish (this typically only takes a few minutes)
  5. Once complete, one of two things will appear on the screen:
    • a No issues found message
    • a brief description of any errors found plus further instructions
  6. If the diagnostics test does find errors, take a note of what they are

Note: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete.

Regardless, take a note of what happens and let me know how you went.

Calibrate your MBP battery

If you're still concerned, you can always calibrate the battery. This isn't officially required on MacBook models with built-in batteries, but some users report an improvement after doing so.

Before following these steps, read over them fully as you will need to leave your MBP in a flat and powered off state for at least five hours, so you may want to time things to suit you (for example, so that it's in that state overnight while you're sleeping).

Follow these steps to do the calibration:

  1. Fully charge your MBP - Since we're unsure about how the OS is reading the battery percentages, make sure you go by the charging indicator rather than the battery icon in the menu bar.
  2. Now use the MBP for a minimum of two hours while it's still plugged into AC power. (Note: You don't have to actually use it, but have it logged in and running off AC power for two hours).
  3. After a minimum of two hours has passed, unplug the MBP from AC power, but do not shut it down. Leave it logged in or use it as normal during this time.
  4. Keep using your MBP (or just leave it running) until it automatically goes to sleep because it's diminished its safe power reserves. If you happen to be using it, you should see a warning that the battery is low. Ignore this.
  5. Eventually your MBP will go to sleep. When it does, press the power button to shut it off fully.
  6. Wait at least five hours and then plug it into AC power and give it a full charge. Once again, go by the charger to know when it's fully charged.
  • Dude, the Apple website says calibration is not necessary: support.apple.com/kb/PH14087?locale=en_US
    – invictus
    Sep 2, 2017 at 5:44
  • This is true, it isn't necessary for built-in batteries. However, you'd be surprised the number of users who believe doing so will rectify how well the battery is measured by the system. Personally, I think resetting the SMC is all you need to do. For extra peace of mind, you could also run Apple Diagnostics as it really doesn't take too long to do - but I wouldn't do that until after resetting the SMC anyway.
    – Monomeeth
    Sep 2, 2017 at 5:50

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