Knowing how much a Mac has actually been used by its owner can be very useful if you’re buying pre-owned. A Mac three years old that’s been used very infrequently could be a better purchase than a two-year old Mac that’s been left running 24/7, for example.
While physical condition of the Mac gives a clue, you can garner some further clues by a little software probing. It’s not entirely accurate, and comes with substantial caveats, but could be worth a try.
Battery charge cycles
This is obviously only of use on a MacBook (including Pro/Air), but the number of times a battery has been charged is useful information. This is represented as the charge cycle figure. A low charge cycle figure on an older Mac means one of two things: either the Mac hasn’t been used much or – and perhaps more likely – the Mac has spent most of its life attached to its charger, so might rarely have left the owner’s home or office. Either way, a low number is good news.
What’s a low number? My current MacBook Pro, which is 1.5 years old and spends half of its life on charge, and half running on battery, has a cycle count of 378. This is a healthy average figure for the age of this computer. Although it’s impossible to estimate, if I saw something like 300 cycles on a three year-old Mac then I would be very impressed. (For what it’s worth Apple considers batteries charged over 1000 times to be in need of replacement, on models sold since 2009 at any rate; earlier models had maximum cycles of 500 or 300.)
To discover this information, hold down Option (Alt on some keyboards), then click Apple > System Information. In the window that appears, click the Power heading at the left, and then look at the Cycle Count figure on the right, beneath the Health Information heading.
Of course, if the battery has been replaced then this info won’t be all that useful – and the best way to find out if it has is to ask the seller. However, on modern MacBook (Pro/Air) models it’s not trivial to replace the battery, so it’s less likely to have happened compared to older Macs.
Note that this setting is a firmware value within the battery itself, so will not be affected by any reinstallation of the operating system. It’s possible it could be hacked but to my knowledge there’s no published method of doing so, so it’s very unlikely to have happened.
Every modern hard disk/SSD records the number of hours it has been used, in hours, and this gives an indication of the number of hours the Mac has been powered-up (provided the disk hasn’t been replaced at some point, of course).
To discover this information, download the free-of-charge smartmontools app, right-click the installer, select Open, then opt to install the app.
Update 25 Jan 2017: Whoops, it looks like the smartmontools installation package is broken. Therefore, you’ll have to install Homebrew using the instructions on its home page, then within the same Terminal window you opened to do so (you’ll find the Terminal app in the Utilities folder of the Applications list of Finder), type brew install smartmontools. If you’ve already tried to install smartmontools via the installer package you’ll need to type the following instead: brew link −−overwrite smartmontools.
Following this, open a Terminal window (which you’ll find in the Utilities folder of the Applications list of Finder), and paste-in the following before hitting Enter:
smartctl -A /dev/disk0
The output might be confusing but look for the row that reads Power_On_Hours, and the the figure listed in the RAW_VALUE column at the very right. You might have to expand the Terminal window horizontally to make everything line-up.
This figure is approximately the number of hours the drive has been powered-up since it was installed in the computer. With my 1.5 year-old MacBook Pro I see a figure of 4607 hours, which translates to the equivalent of 192 days of solid usage – although this was obviously broken-up into periods when I was working. I use my Mac for around eight hours a day (work and play), so if you do the math (548 days * 8 hours per day) you’ll see this figure just about makes sense.
However, it’s not quite as simple as you might expect because modern battery-powered Macs feature Power Nap, which means the computer wakes-up silently even when computer is in sleep mode (such as when the lid of a MacBook is closed), in order to complete various tasks such as fetching email. Because of this, the hard disk might actually be awake even though the computer is not being used, thereby skewing the power-on figure from our perspective.
Note that this setting is a firmware value within the disk itself, so will not be affected by any reinstallation of the operating system. It’s possible it could be hacked but to my knowledge there’s no published method of doing so, so it’s very unlikely to have happened.
Learning when macOS/OS X was installed
If the user you’re buying the Mac from has never reinstalled macOS/OS X then you can find out exactly when they first powered-up the Mac and completed the initial setup. Just open a Terminal window as described above and paste in the following:
ls -l /var/db/.AppleSetupDone
Then look at the date listed in the output, approximately in the middle of the line. On my MacBook Pro I see 28 Jun 2016, which doesn’t match with my 1.5 years of usage of this computer, but probably does mark the point at which I decided a complete reinstallation of OS X/macOS was required. Notably, this date doesn’t change when even major operating system updates are applied.
Do you know of any other clever trick for working out how much a Mac has been used? Let me know in the comments below and I’ll add them in to this article at a later date.