MacBook – What are the best practices for battery longevity

batterycharginghardwaremacbook pro

How do you maximize the cycle count of your battery?

There seems to be a debate between:

  1. Leave plugged in 24/7 but do a full cycle once a month
  2. Charge to ~100%, drain to ~10%, repeat.

NOTE: Taking your battery out is bad

Which method is better and why? How much of a difference does it really make?

Here are some of the better sources I've found about battery behavior so far. Even still I feel they don't conclusively answer the question above. See my elaborations below:

Elaborating on Option 1

Now IF Apple engineers were smart and optimized for AC draw when plugged in to not use up your charge cycles, then it seem logical to assume that you are using effectively none of your 1000 charge cycles while plugged in. If that's the case, it would seem that the LiPo drop from holding at 100% would be vastly outweighed by the fact you're not using any charge cycles.

However, this is a purely speculative assumption and I could find no evidence to either confirm or deny.

If this is NOT true, and the AC adapter only goes to charging the battery, then there would be no difference. Your battery would drain to 99%, then back up to 100%, then back down to 99%, etc. Those micro-charge cycles would add up at the same rate as 100% -> 0% -> 100%, and you would get no gain. In this case the negative effect of holding LiPo batteries at 100% would outweigh everything else.

Elaborating on Option 2

There are lots of good reasons why Option 2 is the way it is:

  • Because of known LiPo chemistry issues, holding a 100% charge for a long time causes the battery to degrade
  • Apple specifically recommends not to leave it plugged in all the time on their website
  • Draining a battery all the way to zero all the time is bad for the cell (Which is why ~10% is used)
  • Heat is a killer, and when plugged in AND charging, you get extra heat that causes damage.

There are a couple reasons why I'm challenging Option 2:

  • It seems silly that the most intuitive use case for thousands of people that use their macs as primary computers is wrong.
  • If the hypothesis in option 1 is true, you're just burning unnecessarily
    through your finite charge cycles.
  • It's a pain to have to remember to keep plugging in and plugging out and be worried about whether or not your device is plugged in.

Best Answer

Final Conclusion Given the sources and explanations below. I am officially going to do the following to optimize my battery life:

  1. Keep my battery as cool as possible.
  2. Don't worry about whether it's plugged in or not. When it doubt, keep it plugged in so it uses AC power instead of battery, unless getting hot.

It turns out that the two methods I originally posited are largely moot. The only thing that really matters is temperature.

"Temperature was the most significant factor contributing to the cell degradation, with state-of-charge (SOC) and discharge pulse length of secondary importance." (Liaw et al.2)

Furthermore, it turns out that the decay can be accurately mathematically modeled:

enter image description here (See Ramadass et al.1 for explanation of terms)

However, the dominant model is that of the Arrhenius formula, which generically predicts time-to-failure as a function of temperature.

The figure below shows the capacity at various cycle counts. Just look at the capacity on the x-axis. The top graph is at 25ºC, the bottom at 50ºC.

After 600 cycles, the cooler battery had ~2x the capacity

Effects of cycling and temperature on Lithium Ion battery degradation

While I could still find no evidence on the behavior of Mac power circuitry, there was helpful information on the official Dell website. Two items specifically stood out.

Q. When docked or AC adapter is plugged into a wall outlet, am I using my battery charge?

A. No.

http://www.dell.com/content/topics/global.aspx/batteries_sitelet/en/batteries_faq?c=us&l=en&cs=19#faq9

Q. Should I totally discharge, then recharge my Dell laptop battery occasionally to make it last longer?

A. No, discharging and charging does not increase the life of a Lithium Ion technology battery.

http://www.dell.com/content/topics/global.aspx/batteries_sitelet/en/batteries_faq?c=us&l=en&cs=19#faq27

However It is important to note that Apple and Dell charging circuits may be different. Although, given that Dell does this, I assume apple does as well. On this assumption, unless someone can provide sources to claim otherwise, I will assume that the Apple charging circuitry is smart enough to know this.

I encourage anyone to continue exploring this question and challenge my assumptions. Please see the sources below if you're curious for a more detailed explanation.

Sources

1 Ramadass, P., Bala Haran, Ralph White, and Branko Popov. "Mathematical Modeling of the Capacity Fade of Li-ion Cells." Journal of Power Sources 123.2 (2003): 230-40. Web. http://www.che.sc.edu/faculty/popov/drbnp/WebSite/Publications_PDFs/Web33.pdf.

2 Liaw, B., R. Jungst, G. Nagasubramanian, H. Case, and D. Doughty. "Modeling Capacity Fade in Lithium-ion Cells." Journal of Power Sources 140.1 (2005): 157-61. Web. http://electrochem.org/dl/ma/204/pdfs/0253.PDF.

[3] Ning, G. "Capacity Fade Study of Lithium-ion Batteries Cycled at High Discharge Rates." Journal of Power Sources 117.1-2 (2003): 160-69. Web. http://www.che.sc.edu/faculty/popov/drbnp/website/Publications_PDFs/Web38.pdf.

[4] Ramadass, P., Bala Haran, Parthasarathy M. Gomadam, Ralph White, and Branko N. Popov. "Development of First Principles Capacity Fade Model for Li-Ion Cells." Journal of The Electrochemical Society 151.2 (2004): A196. Web. http://www.che.sc.edu/faculty/popov/Publications/Premanand1.pdf

[5] Zhang, D., B. S. Haran, A. Durairajan, R. W. White, Y. Podrazhansky, and B. N. Popov. "Studies on Capacity Fade of Lithium-ion Batteries." Journal of Power Sources 91 (2000): 122-29. Web. http://www.che.sc.edu/faculty/white/2000studiesoncapcaityfadeofzhangharandurairajanwhitepodrazhanshkypopov.pdf.

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