If We Assume: The (De-)evolution of My Laptop Battery

Update #1: the GitHub repo for this data/script is now available.

Update #2: this post has now become my most popular, surpassing The United States of Starbucks.Awesome!

Update #3: I have been contacted by Apple Executive Relations regarding the health of my laptop.


Today my MacBook Air is one year old. That's not exactly an officially recognized holiday, but it does mean one thing very cool:
I have one year of data on my laptop battery, recorded every 1 minute of computer usage! Epic

A little backstory: I started occasionally keeping track of my laptop's battery several computers ago. Near the end of my previous computer's life I realized I could automate this collection of data. By keeping a record of the battery charge every minute my computer is being used, I am able to track the health of my notebook, as well as study my own computer usage in remarkable detail.

In a previous blog post I noted that it would only take a negligible amount of hard drive space to keep such a record for the entire life of your computer at 1-min sampling (though I under predicted the amount of space by about 3x). The previous battery study also provided me with subject matter that was included in a quantified-self art exhibition in Ann Arbor last year. While I obsessed about what to buy for this latest computer, battery life never factored in to my equation. Every model seemed to boast more than enough capacity.

Without further ado, here is what 1 year (152,411 samples) of battery capacity data looks like for my 2012 MacBook Air:

Look at that awesome sampling! I use this computer as my work and home machine. It's actually my only regularly used computer (big monitors are for wimps). I try to take good care of the computer, cleaning it, letting the battery cycle, keeping the harddrive with lots of space.

When you fold my computer usage over a 24 hour period, looking at how frequently the notebook is in use (ignoring the battery data), you get this wonderful diagram:

Bam! You can clearly see when I'm (usually) sleeping, and my diminished use of the computer around dinner time. 

This figure can be taken to the next level (I've shown versions of this in my previous posts about computer batteries). Here we have the logs folded over Time of Day as a function of time, one little dot for every minute the notebook is in use.
Now we've got some good trends! Normally I'm very regular about starting my day and taking a break for dinner/relaxing in the evening. A notable change in behavior occurred at Days=300-ish, when I started my summer internship at Microsoft Research (they happily provided me a computer for work). At Days=345-ish I went on a proper vacation, and didn't open my laptop once! I haven't opened my laptop since last Friday. My soul feels better — James R A Davenport (@jradavenport) August 9, 2013
But back to the battery life, and here's where it gets really interesting! I've noticed my Air's battery just ain't quite what it used to be. When I compared the record of battery capacity with that of my old MacBook Pro, my jaw hit the floor:

Comparatively the Pro destroyed my newer Air! Even though the sampling is quite sparse for the first year, the Pro's trend was clearly more flat. My usage behavior is basically identical. Both the Pro and the Air were my primary (only) computer being used at home and work. Both computers were being used for astronomy grad school.

My current battery cycle count is 223. My MacBook Pro got to around 750 before I replaced it, roughly  giving the same number of battery cycles per year as now. According to Apple, the Air's battery is designed to last 1000 cycles at 80% capacity, nominally over 3 years (length of the Apple Care Warranty I purchased). Based on this figure, I'm skeptical that it will reach this target. Further, if I took it to the Apple store for inspection, it's not clear to me that any problem would be diagnosed (to be clear, the computer is working wonderfully thus far, absolutely the best Apple notebook I've purchased in the past decade)

So what's changed? My usage is the same, as far as I can tell. Some others have reported issues, describing dramatic battery decay in 2012 era Mac notebooks. Maybe these new batteries are just not built as well? My MacBook Pro had a capacity of 4600mAh, while the MacBook Air boasts a factory capacity of 6667mAh. Perhaps the engineering required to provide 45% more power for a computer almost half the size means the battery isn't as durable.

What ever the reason, I'd love to know:
A) what kind of performance are other people getting out of similar aged notebooks?
B) what is Apple's response to such issues?
C) are there other similar datasets available for comparison?

The MacBook Air has been my favorite Apple computer yet, I can't see myself going back to a bulky full sized laptop ever again. Maybe these new "all day" batteries won't have this problem. Happy birthday, computer.

The GitHub repo for this data/script is now available.