Battery Health

philfry

macrumors regular
Original poster
Jun 22, 2010
152
151
So my 2017 had a swollen battery. They asked if I keep it plugged in all the time. I said most of the time it’s docked. He proceeded to tell me that this is bad and I should have 200-300 cycles after 2 years. I had 76.

What do you think? Is leaving it plugged in being bad a myth? Did I just win the bad battery lottery?
 

mightyjabba

macrumors 68000
Sep 25, 2014
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255
Tatooine
I don't think there is any definitive answer. Many people here will say that it doesn't matter, but anecdotally I've found that I ended up with a swollen battery twice on my 2014 MBP that was used as a desktop. 76 cycles doesn't seem that out of line though -- mine was actually much less than that.
 
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robvas

macrumors 68030
Mar 29, 2009
2,945
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USA
Use mine 90% of the time plugged in, never had a battery swell up over 10 years. I think it's just the luck of the draw.
 

konqerror

macrumors 65816
Dec 31, 2013
1,495
2,475
So my 2017 had a swollen battery. They asked if I keep it plugged in all the time. I said most of the time it’s docked. He proceeded to tell me that this is bad and I should have 200-300 cycles after 2 years. I had 76.

What do you think? Is leaving it plugged in being bad a myth? Did I just win the bad battery lottery?
Swelling is enhanced because you're keeping it at a high state of charge all the time. 80% is apparently the magic number (keep in mind that Apple soft-caps battery capacity to enhance lifespan).

Here's the science:

Gas generation (namely, the volume swelling of battery, or called the gassing) is a common phenomenon of the degradation of battery performance, which is generally a result of the electrolyte decomposition occurring during the entire lifespan of Li-ion batteries no matter whether the battery is in service or not. Abuse conditions such as overcharging and overheating make the gassing worse or even result in disastrous accidents.
...
Assuming that the Li-ion battery is well formed in manufacture and properly operated in service, the gas generation can be attributed to the chemical decomposition and redox decomposition of the electrolyte solvents on the anode and cathode.
...
In particular, the chemical decomposition is increased with the temperature, and the redox decomposition is increased with the state-of-charge (SOC) of battery.
...
For the gas generation caused by the redox decomposition of electrolyte solvents on two electrodes, Figure 1 shows that the swelling ratio of a graphite/LiCoO2 cell remains nearly constant when the SOC is lower than 80%, however, dramatically increases as the SOC exceeds 80% (Lee et al., 2003).
 
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Sanpete

macrumors 68020
Nov 17, 2016
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Utah
So my 2017 had a swollen battery. They asked if I keep it plugged in all the time. I said most of the time it’s docked. He proceeded to tell me that this is bad and I should have 200-300 cycles after 2 years. I had 76.

What do you think? Is leaving it plugged in being bad a myth? Did I just win the bad battery lottery?
Who's they/he? Apple doesn't offer any such advice.
 

konqerror

macrumors 65816
Dec 31, 2013
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Who's they/he? Apple doesn't offer any such advice.
I got the same lecture from the Apple store when I took in a 2016 with a swollen battery and they said it was technically abuse but they'd cover it "this time" (common store strategy).
 

Mr Screech

macrumors member
Mar 2, 2018
47
80
I have 250 cycles after 8 years. No issues here, battery capacity is at 82%.
I'd guess bad luck on your side, but don't know about the >2016 series mbp's.
 

maflynn

Moderator
Staff member
May 3, 2009
65,626
31,760
Boston
What do you think? Is leaving it plugged in being bad a myth?
As with many battery-related questions, the issue of keeping your laptop plugged in when it’s reached full capacity is hotly debated, and so there’s nothing wrong with turning your machine off and unplugging it. If you’re going to store your laptop for an extended time without using it, then discharge or charge it to 50 percent before putting it away.
If a laptop is plugged in all the time, the battery is working harder than it would be if it was slowly cycling between 40 percent and 80 percent.
If that last piece advice made you feel guilty, don’t worry about being so basic with your laptop use. Keeping your laptop plugged in regularly, with the battery charged to 100 percent, isn’t slowly killing it, despite what you may read. It’s only as bad as charging it once, to 100 percent, in the first place. Once the battery hits 100 percent, most modern laptops stop charging, and the power is diverted to the system instead.
Did I just win the bad battery lottery?
Did I just win the bad battery lottery?
Is apple quality that bad now that people are winning battery lotteries, cpu and display lotteries? :oops:
 

Sanpete

macrumors 68020
Nov 17, 2016
2,352
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Utah
I got the same lecture from the Apple store when I took in a 2016 with a swollen battery and they said it was technically abuse but they'd cover it "this time" (common store strategy).
I don't doubt that there are people working at Apple Stores with such ideas, but Apple itself doesn't give such advice. Here's their page on it:


My own 2016 15" has 7 cycles on it, capacity 6575, which is probably fine for one over three years old.

I almost always have my MBPs plugged in. The only swollen battery I've had that I was aware of was on an Alienware M15 that was just a couple weeks old. Got the battery replaced and it's been plugged in for months now with no more trouble.

But that's just my experience. I don't know more than that and what I read.