I have two mid 2012 MBPs. Sometime last year they both started randomly shutting down and showing the 'please plug me in to power' image when trying to start them up. That would be fine if the batter was at 1% or less but this happens when the battery is at anywhere from 30% to as high as 48% full. The power cycle info says 500 cycles or so. Both of them do this. They are both patched current, always. I asked Apple they suggested NVRAM PRAM and SMC reset, as expected, which had no effect. Any ideas?

  • Alas none of the answers posed seem correct. For two machines to have been affected in the same way at the same exact time seems unlikely if it's a battery failure especially given the drastically different usage patterns on the two.
    – Ram
    Commented May 20, 2016 at 23:44

3 Answers 3


Your battery is shot.

A battery's life is determined more by age than the number of cycles. Yes, number of cycles do play a part, but the biggest culprit is age. In short, you have a 4 year old battery. A 4 year old battery that was never used is going to perform about as well as a 4 year old battery with 500 cycles.


As far as what you are seeing, this is not an abnormal symptom. Your MacBook Pro has no sensor to be able to determine how quickly a charge will dissipate within the cell. All it can do is measure the voltage under load and calculate how much charge is left.

As your battery ages, there is a build up of the solid electrolyte interphase (SEI). This layer is what "transfers" the electrical charge from the chemical reaction. As this layer builds, the performance degrades. This layer continues to build from the time the battery is manufactured until the time it is recycled. There's no stopping it.

In short, your MBP is calculating that you have 30-40% of battery left; it's only a calculation as it cannot account for or measure the SEI layer buildup.

Just to provide you a reference, I am working on a Dell Precision M4300 laptop (installing FreeBSD). The battery reports 100% and healthy. If I unplug, I get about 30 seconds before the battery dissipates and the laptop turns off. So, I have the same symptoms you do, except it's happening at 100% charge. This laptop and battery are 8 years old so the behavior is not unexpected. What would be unexpected is if the battery held any charge at this point.

The Good News

It's pretty easy to fix. iFixit.com has an excellent guide: Battery and Trackpad. Disassembling MacBook Pro 15" Retina 2012-2015 and the prices are relatively low (less than $45 on Amazon).

Disclaimer: I have personally used two of these exact model batteries on MBP's and both are still running strong.

  • Thanks Alan. That makes sense, in general. I've seen the behavior you describe on previous devices. Here's the key difference -> when it shuts down at 40% power level and demands to be charged, all I have to do is plug it in for 60 seconds and it will wake up and run for a few more hours.
    – Ram
    Commented May 13, 2016 at 18:34
  • Based on your last comment, I would bet a dozen doughnuts that you have at least one bad cell in the bunch. You might have 40% charge, but because the one bad cell drops so quickly your MBP reacts as if the whole battery died. Basically that one cell can probably hold a 20% charge, when it goes, it goes fast!
    – Allan
    Commented May 13, 2016 at 19:13
  • Thanks @Allan. Are you saying that one bad cell in the battery pack would result in OSX deciding that at 48% the battery is dead but then when I plug it in for one minute and unplug in the batter will last the remaining three+ hours?
    – Ram
    Commented May 13, 2016 at 20:51
  • At least one cell...it's not so much the OS is "deciding" it's that the OS detects a charge one minute then the voltage isn't there the next to keep it running so the hardware shuts down. More like it's "tricked."
    – Allan
    Commented May 13, 2016 at 20:54
  • 1
    This still doesn't explain it AFAICT. If you're right then when I plug it in and let it charge for one minute then it might be willing to power on but it would not stay powered on for three hours since OSX would again 'realize' that the pack is dead and shut it down.
    – Ram
    Commented May 15, 2016 at 22:43

You battery is dying!

4 years is usually average when a battery starts dying.

I would personally take it to the Apple store, have them look at it. They will tell you if it needs replacing. I would just get it replaced at the Apple store, the price difference is not to much and you know you're getting a good battery.

Replace it ASAP, as there is a chance the battery will start to swell and damage other components in your computer.

If you can download Coconut Battery and give us a screen shot:

You can also: 1. Click on Apple logo at top left 2. Click on 'About this Mac' 3. Click on System Report' 4. Power on the left

You will then see a few lines related to battery information like this

Cycle Count: 
  • I'm having a similar problem with a 2011 MBP. I keep it on the charger 99% of the time (I use it mainly as a desktop). But when I travel and use it on battery power it dies around 30%. Health information says "Cycle Count: 67 Condition: Normal"
    – Barmar
    Commented May 14, 2017 at 16:45
  • @Barmar It's ability to hold a charge degrades over time even if the over health is good. Download Coconut Battery and see what its charge capacity is at. If you want additional battery life, you should replace it. And going forward try to cycle your battery a little bit, let it drop to 60% once or twice a week and back to 100%.
    – Rio
    Commented May 15, 2017 at 15:58
  • I've been using Battery Health Monitor for many years. Is Coconut Battery much better?
    – Barmar
    Commented May 16, 2017 at 15:46
  • Just tried it. Coconut Battery gives essentially the same information about the current status, but the historical info is nice. Current capacity is 5886 mAh versus origial capacity = 6900 mAh.
    – Barmar
    Commented May 16, 2017 at 15:52

I had a consistent 20% shutdown. My battery was inflated and I got it replaced by Apple for 250€. However, even with the new battery, it shutdown exactly at 20%. Resetting the PRAM - CMD+Shit+P+R before boot - did the trick.

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