More RAM = Less Battery Life (& Vice Versa)?

My laptop (Linux PC) was originally configured with 1x4gb and during this time I didn't really record any battery life performance. I then added another 4 gb stick so I can access dual channel so it went to 2x4gb (non matching sticks, same type and ranks). I have been using this configuration for about a year and the battery life on a full charge averages about 3.25-3.5 hours of battery life.
I got a different computer a decided to use that 8gb on the other system and downgraded the original laptop with the 8gb to 4gb (2x2gb).
I haven't done any BIOS update or anything at all from the switch and I noticed my battery life shot up a little to over 5 hours of battery life. Keep in mind, I don't even go above 4gb of RAM on either configuration. I am constantly aware of my swap, so therefore I'm not using any of my HDD's access memory.
That is a significant difference, so I searched it up. A lot of Mac users have been experiencing the same thing (not many PC users have wrote about this or maybe there are a lot more Mac users who care about their battery life?)
15" rMBP 8GB vs 16GB RAM battery life difference - MacRumors Forums
http://forums.macrumors.com/showthread.php?t=420564

Short summary:
2x4gb (non-matching, same ranks same type PC3-12800 1600): 3.25-3.5 hours
2x2gb (matching, same type PC3-12800 1600): 5.1 hours
I keep hearing that the battery life is negligible as the RAM slots will consistently draw 1.5v (given that I was using two slots the entire time).

Has anyone experienced this?

 

I haven't, and if I did it was probably only a few minutes difference at worst. Really, it's just statistical noise and I doubt that messing with your RAM configuration is the sole cause of your battery life differences (or even a major factor). Are you sure you didn't do anything different in addition to the RAM reduction (including using your computer slightly differently)?

 

On the PC side, 2GB (2x 1GB) to 4GB (2x 2GB) or 8GB (2x 4GB) was only ~10 minutes less.

With 8GB SoDimms, I haven't used a computer yet with less then 16GB RAM so I can't say for IB or Haswell systems; but I'd be surprised if the difference is more than the older platforms (~10 minutes).

What more RAM has done in every case is give a more responsive system (even/especially for HDD's) and a platform with much more potential for productivity for a given amount of battery power.

More time off the mains means nothing if you can't actually use the system for useful work.

On the MAC side; no clue on the efficiency - but the couple of MBP's I have helped upgrade showed a tremendous productivity and responsiveness increase that easily offset even the battery life differences you report. (Assuming you want to do work with the system and not just want it available, but idle).

 

Every time I'm on battery, I always lower my back light panel to the lowest brightness and to achieve better battery life. I haven't use my computer any differently. If I did, I would have considered it. Additionally, shouldn't battery life decease when going from 2x4gb to 2x2gb anyway? I definitely feel and improvement in battery life. Even after rebooting.
There is definitely something to this. I have never seen my battery life indicator offer anything above 4 hours.
I'll try to use this configuration for a while and compare my experience.

 

Test and see (I'm curious too).

I wouldn't be surprised with Apple that they have an O/S that is setup differently with different amounts of RAM.

(They might assume a 'casual/consumer' user with 4GB RAM or less and a 'power' user with 8GB or more)?


Looking forward to your next report (in a week or so).

 

That would be an interesting idea, considering that Apple uses the same hardware as everyone else. The only real difference should be in software.

Just looking at the numbers, a single DIMM uses a trivial amount of electricity, compared to other components, so just a simple hardware switch doesn't really explain the battery life difference, assuming the same battery, same time period, same usage behavior, etc.

 

I've tested it on my notebook full drain from 100% to 5%. 1x4GB or 2x4GB or 2x8GB resulted to be within 10 minutes of each other. Only case where it MIGHT make a difference is in an already low powered netbook, even then you have to do the math, going from 3.5 to 5 hours that RAM configuration would be consuming 40% of the total system power. Not realistic.

 

By battery life, do you mean the computer actually lasted a lot longer before the battery died, or were you just going by how much remaining battery life Windows said you have?

 

What is the laptop that we're discussing here to begin with?

 

Dell Inspiron 3521
Pentium 1.8 GHz 2117U (3rd gen Ivy Bridge integrated Intel HD Graphics)
Manufacturer claimed 4 hours

I'm going to do a slow discharge on the battery before I do a little testing. With GNU/Linuxs' power managers, I can record the battery's history and statistics based on charge %, discharge %, time to empty, discharge profile, and discharge accuracy based on a 1 week interval. For self accuracy, I'll also do a self recording based on the Wh left so I can eliminate minute program differences.

 

Without getting too complicated, the easiest way is to just use something like the ReloadEvery add-on for Firefox and set up a few tabs and let it run from 100% to 5% and shut down or hibernate.