4

Tl;dr

My 2015 Macbook Pro Retina shuts off without any warning when the battery discharges to 75%.

According to Coconut Battery

Design Capacity: 56.7%

Made in 4/13/15

Has lasted 3,268 cycles, and the battery status is apparently 'Fair'. Simplo made my battery.

macOS Mojave Experience

I've recently started to notice a decline in my battery when I decided it would be a 'good' idea to upgrade to Mojave. Long story short: it wasn't. I have 2 desktops with dynamic wallpaper (changes throughout the day), and most of the time I leave my Mac asleep (8 hours~) to reopen it, the trackpad is hard: Macbook is dead.

macOS High Sierra Experience

On HS(10.13.6), the battery used to die at around 30-40%, which to me isn't as bad. When I opened it after it's 8 hour break, it shows me the login screen (takes a couple 4-5 seconds to wake up). Note that on Mojave, if it did survive the 8 hour nap then it woke up immediately; and I store my Mac in a cool place, the bottom feels slightly warm. Power nap is off for both situations.

Battery Issues

Recharging boots it up and shows me anywhere from 64% to 75% battery left. I've also noticed a bunch of battery glitches in the top menu, and whenever I charge it'll show me 45% then quickly switch to the 'real' percentage.

Before someone tells me to 'reset your SMC', I will point this out: System Report > Controller returns that there is no controller. I have tried resetting the SMC twice and it did reset (indicated by power adapter turning green then orange) but had no effect on the battery.

I'm not sure about getting a new battery, as I may be getting another Macbook later this year, so blowing $100 on a new battery for a 6 year computer I may not use for a long time is not a financially smart decision.

I have also forgot to mention this, but when my Mac reaches 100%, Coconut Battery says it can still be charged, and it actually can. When I "overcharge" it at 100%, turn off the charger it takes significantly longer to get from 100% to 99% if I were to just stop charging directly when 100% is reached.

So, what can I do so my Mac dies at 56% instead of 70%~?

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  • I wonder if overcharging it has damaged it. In addition, letting it run out overnight each day is adding considerably to your cycles. Letting it trickle charge + run off main overnight (really, whenever you can) is better for the battery I think?
    – Tim
    Oct 2, 2021 at 8:26

3 Answers 3

15

Typical life expectancy ("Maximum cycle count") is 1,000 cycles. From Apple's webpages: "Your battery is designed to retain up to 80% of its original charge capacity at its maximum cycle count. For best performance, replace your battery when you reach its maximum cycle count."

In short: your battery has been heavily used and needs replacing. I'm surprised that the OS hasn't given you a notice that the battery needs servicing. It just isn't reliably holding charge.

Apple defines one cycle as a complete 100% - 0% discharge; and this also includes partial discharges cumulatively, so a discharge to 75% (before recharging) is 0.25 towards the next cycle.

If the data is to be believed, in six years, you've managed an impressive average of a complete discharge from 100%, then a recharge and another 50% discharge, every day.

There's nothing else that can be done to improve it.

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  • Is this true for androids too? (To be precise: Samsung Galaxy J1 Mini Prime 2016) Oct 1, 2021 at 17:56
  • 2
    All rechargeable batteries degrade with time and with use. So yes, this is true for Android devices, too.
    – longneck
    Oct 1, 2021 at 18:36
  • I find this answer interesting, Coconut Battery considers by battery fair; and not once have I seen my Mac freak out about the battery, the current status is 'Replace Soon' and never anything beyond that.
    – SomePerson
    Oct 3, 2021 at 23:03
  • @SomePerson If you've seen a "Replace Soon" indication, then that means it needs replacing. There's no shades of urgency. TBH, I would consider Coconut Battery's suggestion that the condition is 'fair' to be extremely suspect, given that it's over 3 times the expected lifespan.
    – benwiggy
    Oct 4, 2021 at 6:51
  • I swear my mac is playing mind games with me: it died at 95%, shows up as 89% on reboot; coconut battery after that shows 41.5% design capacity & battery says 'Replace Now'... I look at it right now and it reverts back to 56.3% and 'Replace Soon'. Will take as accepted answer-- apparently my mac will be a hand-me-down so the battery shall be replaced.
    – SomePerson
    Oct 7, 2021 at 7:17
3

There is a Battery Recall Program for some MacBook Pro 15" Mid 2015.

You can check if your device is eligible on https://support.apple.com/15-inch-macbook-pro-battery-recall

2

Distinguish your battery cells actually holding that amount of charge from the battery controller IC's estimate of charge, which appears to be off. Due to the very flat discharge curve of LIon cells, charge is estimated by measuring the charge flowing into and out of the battery, and estimated charge capacity will be updated over time as well. The controller may have failed to properly track charge, or to update its estimated charge capacity as quickly as it has degraded, OR the battery may be self-discharging.

Suggested: feel the battery, especially just before and after charging, and perhaps 15..30 minutes in. Is it hot? If so, I will suggest treating this as a potential safety or equipment damage issue.

Your battery cells are worn out and need to be replaced.

When ordering a replacement battery, beware battery packs that were manufactured around the same time as the original.

Also beware "jump-started" LIon batteries. I've seen the aftermath of that. Once an individual cell discharges below (IIRC) 1.4V, the copper anodes start to go into solution. The battery controller thus disables the battery pack -- but this can sometimes be reversed by "jump-starting" the pack. Charge them up: copper plates out as nucleation sites, then lithium whiskers begin growing whenever the battery is charged. Eventually, they may puncture the cell membrane and you can have a battery fire.

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  • In order to resolve the difference between the BMS’ estimate of battery capacity and the actual capacity, run the machine through several charge/discharge cycles. Leave it on and running until it shuts off. Then, without recharging, try turning it back on. Repeat until it won’t turn on. Now charge it all the way to 100%. This is one cycle. Do several of these cycles. You should find that the machine shuts off closer and closer to 0% indicated as the BMS learns the battery’s actual capacity. Oct 3, 2021 at 0:26

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