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I have a relatively new MacBook Air (Retina, 13-inch, 2020) just under 1 year old with only 66 cycles reported on the battery.

Question: If I have to1 leave it for several weeks powered-off and completely unplugged from anything and WiFi turned off, is there any information out there as to roughly how far the battery will drop?

Will the total drop divided by the total number of days be perhaps 0.5% per day? 1%? or even 2%? Are there any benchmarks or sources for this kind of information?

Why not check it yourself?

Right now I use my laptop very regularly and just don't have any opportunity to "experiment" on it turned off for a whole weekend much less a week, and there's always the possibility of a little nonlinearity and/or offset at the upper limit.

1This is not a hypothetical question! I will be needing to do this at some point and would like to have some expectation of the outcome ahead of time. Finding one's self with a low battery and no means of charging it is an issue that a Stack Exchange question can't address.

I'm also curious if there anything inside that would actually draw enough current that would impact the battery's otherwise natural rate of loss, but that's probably a separate question.

uhoh
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  • Does’nt Apple give a standby time? – Solar Mike Jun 27 '21 at 10:38
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    @nohillside For those that travel there is also the contingencies related to not being able to find an outlet when you need it, or the right adapter (e.g. someone "borrows it" and forgets to return it) or a cable getting damaged. – uhoh Jun 27 '21 at 15:16
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    @SolarMike Not when your mac is switched off. (OP mentions that it will be powered-off). – sfxedit Jun 27 '21 at 17:47
  • See https://apple.stackexchange.com/questions/216805/will-my-battery-get-harmed-if-not-used-for-long-time for the answer. Several weeks is nothing - just turn it off when about 50% charged. – Gilby Jun 27 '21 at 23:35
  • @Gilby there's nothing there that actually states how much charge will remain after six months though and a lot has changed in both hardware and software since 2015. One might infer something from that wording, but for the purposes of this question I'm really looking for a number for the 2020 model. One may or may not be forthcoming, but let's wait and see. Thanks! – uhoh Jun 28 '21 at 01:27
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    Most modern electronic devices, including all Apple portables in recent history, are never truly "off". There are supervisory ICs that remain powered as long as there is a power source, whether it's AC or the primary battery. Apple portables also contain either a backup battery or supercap for when the primary battery fails. In the 2020 MBA, which is built around M1 silicon, there is an Always-On Processor (AOP) that performs power management functions, among other tasks. While quite efficient, this draws a small amount of power. So it's more than just the battery's natural leakage at work. – pion Jul 09 '21 at 22:50
  • @pion Thank you for that! I have noticed a "99%" once or twice after my 2020 laptop sat powered off for a while (about 1-2 days), which is something I'd never seen happen with my 2012 laptop, but I wasn't sure if it was just because the software/hardware/firmware had a different way of rounding off or not. If I ever get the chance I'll perform a controlled experiment for several days. – uhoh Jul 09 '21 at 22:58
  • The only real way of getting accurate data is to open the device and attach a current probe and let it run for a few days. You'll see the trend then. (Though, as you wisely point out, there can definitely be nonlinearity over longer timescales. But you'd get a ballpark number at least.) – pion Jul 09 '21 at 23:02
  • @pion I just checked again, it is a "MacBook Air (Retina, 13-inch 2020)" with a "1.1 GHz Quad-Core Intel Core i5" which isn't an M1, but the system certainly might have more activity while powered off than the 2012. – uhoh Jul 09 '21 at 23:06
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    @uhoh Yes you're right, I was thinking of the 2020 MacBook even though you specifically mentioned the Air. The MBA has a T2 chip, which also has its own AOP as well as several other cores which are normally on even while the Intel side is off. I suspect the MacBook is slightly more efficient than the MBA for that reason (but I don't have any numbers to back that up - just a hunch). – pion Jul 09 '21 at 23:13

1 Answers1

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A battery’s dissipation rate depends on several factors like

  • quality/condition of the battery
  • Ambient temperature
  • Charge level at time of hibernation or power off
  • Whether you power it off or only sleep it

This is by no means a comprehensive list; just the obvious factors. The current condition of the battery is quite frankly an unknown since nobody but a qualified technician (scientist) can accurately measure the SEI layer to quantify this.

The other factors you can measure/record with some degree of certainty but insofar as there being some formula or study, you aren’t likely to find one. Each battery ages differently due to the vast differences of how people use and treat their machines.

To get a good estimate, you would need to base it on experience with your MacBook. However, in my personal work experience, I have had laptops (pre Li ion) sit in storage for 4 to 6 weeks (school laptops) and hold a majority of their charge.

One caveat is whether you sleep or power off your machine. If you have no use for periodic updates and checking of messages (see Power Nap) then you should power off to minimize the dissipation rate.

For a reasonable estimate, I personally have current (2019 - 2021) era laptops from Microsoft Surface and a MacBook Air maintain a full charge for well over a month of non use and not being plugged in. Your “several weeks” should be fine.

Allan
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  • Thanks for your encouragement! I'm surprised that there's not any hard information this, but perhaps there are so many variables (battery status, exact model and processor, perhaps even OS) due to the amount of things going on even during shutdown mode, a single number is not possible without actually doing the experiment and leaving one's laptop shut down for a week. – uhoh Dec 18 '22 at 02:12
  • fyi here's another question that is challenging to answer with certainty. Once again there is a "guess" that my laptop would not discriminate between a charger and a battery (even though it certainly can and does communicate with the unit via USB and knows what it is) but as far as I can tell, nobody knows for sure. Also see the associated meta question. – uhoh Dec 18 '22 at 02:31