Does more RAM harm battery life?

Aye, I’m debating between getting 8 or 16 GB or even 32 GB of RAM.
I’ve used 8 in the past but tech does keep moving forward.
Battery life is important to me. Does less RAM = better battery life?

Note: I understand, that you can also upgrade RAM.

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As I understand it, more memory will either have no difference to a positive impact on battery life while the machine is running. This is because there is likely to be less of a usage of the swap disk (writing to/from your disks when memory is low).

More memory may slightly impact battery life negatively while the machine is suspended because more memory takes a bit more power to keep alive while suspended.

Best case: no difference.
Worst case: a little more battery life while running, a little less suspend longevity.

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Don’t bother too much about it, there’s probably no difference, and if there’s one it won’t make much difference. + if you use heavily your machine you might even save a bit of power by having more ram, just like @dc3p said you’ll probably eat more power by using your swap partition/swapfile than by just having enough ram for what you’re doing.

Indeed, don’t bother: This outdated source indicates 0.08W/GB on idle, and 1W/GB max. Outdated here meaning that modern components are likely more efficient.
Although I suspect that the author was mislead what “idle” means. I think RAM can only be idle when suspended to disk, as it always has to refresh its content.

This source here’s more intersting, it claims (again, dated values, but in general should hold true)

Interestingly the amount of RAM has little or no effect on power consumption of PC components. A stick of 4 GB DDR3 RAM will draw about the same amount of power as a stick of 8 GB DDR3 RAM (assuming that they have the same clock speed).

So, if you really care, look up the power consuption of both, the 8 and the 16GB module in question.

Finally, I think you’re both mislead on swapping. It’s not like in the nineties, where swapping involved motors :wink:
I’m pretty sure, the slight amount of extra energy your SSD consumes to write a few gigabytes will always be less than the energy an extra 8GB of RAM will use, as the former is occasional, the latter is permanent.
And if you have a scenario where this is not true, then you’re doing it wrong :wink:
It’s a laptop, and if it has a need to even occasionally swap, you’re doing something you shouldn’t to anyway while not plugged in. Specifically, if you swap, it is very likely your CPU is currently burning way more energy than all other components combined.

@gvbhjn: If you don’t know for sure you need lots of RAM, I’m pretty certain you’ll be fine with 8GB and wouldn’t notice the extra RAM. Likewise, you’d hardly notice the extra energy consumption.
Want to save energy?

  • have some CPU/RAM/swap monitoring widget in your info area (did I mention how I love KDE Plasma?)
  • Make sure no unneeded apps are running, especially no unneeded background daemons
  • Use a browser with an ad blocker (seriously…)
  • Turn the backlight down. This will most likely be the single most effective thing you’ll do

Well I might have been a bit misleading here because I assumed that when you use swap you do it on a HDD since it can harm your SSD, and HDDs does use more power than SSDs.

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The advantage of an HDD is that you hear swapping, and therefore notice something is wrong. IMO it should never happen in normal use.

OTOH, on modern SSDs, you should be unable to damage them by writing 24/7. If you can, it was a bad one. Also, if you swap that much, again, something is wrong IMO. :sunglasses:

I’ve certainly always gone with the principle that, up to a point, more RAM is better for battery life because it will either decrease the incidence of swapping or increase the memory available for disk caching, thereby saving on disk reads. I would think this is true whether using mechanical or solid state storage; reading and writing those non-volatile bits surely has to take more energy than running an extra stick of RAM. (If not, why do NVMe SSDs get so warm compared to sticks of RAM?)

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For users who ask such questions, that point should be way below 16GB :wink:
Users, like the OP, who don’t identify themselves as power users having a need for lots of RAM to do video production or compile LibreOffice from source while being on the road, 8GB should be good.

The most likely case how “ordinary” users fill the swap is by opening more than 3 tabs in the browser (beware, slight irony here. You might be able to open a few more :wink: )
This is a rather passive swapping mode: Write old tabs out, read them back weeks later when accidentally closing the browser… :wink:

I doubt the former part, unless you can provide real numbers (seem hard to find).
Writing should take substantially more energy than reading, as indicated by the name “flash”.
But then again, 99% of the time, the “disk” is neither reading nor writing, for average use cases.

At this point, the idle power consumption is way more important. Tom’s Hardware hints that this ranges from 0.2W to 0.8W, which is quite a difference. During an 8h work-day, it is a difference of up to 4.8Wh, which is more than 10% of a Librem 13 battery.

This very outdated article hints that I/O should be 1…3W. For most people, who typically write less than 10GB per day (200s @500MB/s), this doesn’t even matter. To burn 4.8Wh, you’d have to r/w ~2,700GB (*), but while doing so, I’d worry more about the CPU power needed to process that data.
(* As the article assumes 80% reading, that is not quite correct, as reading should take little energy. Possibly you can write 1000GB the most, but still)

More RAM possibly takes more energy as more cells need refreshing. But the clock speed of the RAM might have a bigger impact.

In general I’d say:

  • If one worries about battery life on the road, most likely they don’t want to do swappy workloads
  • selecting energy efficient components (SSD, RAM) possibly has more impact than the difference between 8GB and 16GB RAM
  • Dimming the backlight has probably also more impact :wink:

ram disk ? @gvbhjn do you need it ?

My response was predicated on my natural assumption that the OP had competently evaluated that they needed 16GB, but that they were prepared to compromise by installing 8GB if it would save battery life. With hindsight, perhaps this was a bit of an odd way of looking at it.

So, what I was really saying was that having enough RAM for your workload might improve battery life. Hence “up to a point”. Too much RAM would worsen battery life.

I so would absolutely agree that there is no point in installing 16GB if you only really need 8GB, but if you actually need 16GB then I think installing 8GB would worsen battery life, not improve it.

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