Understanding Laptop CPU Performance & Battery Use Differences

I have a laptop with a Core i5-2520M. This has a Passmark benchmark of 3536 and a max TPD of 35W. I want to get a new laptop that has at least 25% higher performance and a lot longer battery life. I've examined Passmark ratings and TPD ratings and it appears I have two main choices:

a) Get a 35-37W Quad Core Processor with twice the Passmark benchmark as my current CPU and about the same power consumption. Examples: i7-4712HQ (Passmark 8270 37W), i7-3632QM (7004 / 35W)

b) Get a 15W Dual Core that has roughly half the Passmark. Examples: i7-4510 (3951 15W).

I'm mainly a business user but I will eventually be doing some video editing so I'm leaning towards the quad core.

Seing that the max TPD of the Quad Core is about the same as my current CPU. All other things being equal (power draw of the other components and battery capacity), would I still get longer battery life because on average the newer Quad Core will not being using all cores so the power consumption for the same tasks (web browsing, etc) would be less than the older i5 with the same max TPD but with half the Passmark?

I read somewhere that a lot of laptops or apps don't even take advantage of the four cores? Is that true?

Basically I need to confirm the Ivy Bridge i7 Quad Core is essentially much more energy effecient than my older Sandy Bridge i5. Either I want signifanctly better battery life with the same performance when the i7 isn't using all the cores, or, siginificantly better performance for CPU intensive operations but with about the same power draw. The specs seem to indicate that but I'm not sure if everything works out linearly as I'm assuming?

There is more to look at then passmark scores and max tdp, but you are on the right track.

Laptops obviously use batteries for a power source when not connected to an power source. These batteries can make a 2x difference in your life of the laptop. These batteries can come in different "sizes" - i.e, 6cell or 12 cells. The 12 cell will literally hold 2x more power for your laptop. Plus if you get a used laptop, the old battery will gain cycles and degenerate over time, so it is not bad to buy a new battery every so often, depending how much you use your laptop.

Then you should consider what uses power in the laptop. This includes your screen, cpu, hard drive, cd drive, ram, etc.

Really if you want to save power I would do this:

Screen: Get an led screen over an lcd on a laptop. And try to set it to the lowest brightness that you need at a given time. Also maybe set your screen dim/off to be around a minute of inactivity.

CPU: Set your cpu to be in power saver mode in Windows. This will try to downclock your cpu to run at a minimal frequency rather then at the stock voltage/freq. Like my laptop runs on a i3-2310M (max 2.1GHz) but is currently at 798MHz since I am not doing any major rendering, etc.

Hard Drive: Buy an SSD if you can afford it and replace your mechanical drive. Especially some SSD's use ~ .06W where as a normal 2.5" 5400RPM drives uses ~1W. May not sound like a lot, but when your discharge rate is 15W/h, it makes a difference. Plus it will make everything running quicker/smoother which is especially nice on a laptop.

CD Drive: You may not realize it, but the CD Drive uses power even when it is not in use. Mainly since it is in standby and has to check occasionally if it has a CD in it. Honestly, I took my CD Drive out of my laptop and jst use a USB one if I need one. But you can also buy newer slim laptops with CD/DVD drives.

RAM: This one may not be practical for you, but I replaced my 2*2GB sticks of ram to 1*4GB stick of ram. I have the same amount of storage but only use one stick. I am not sure what the power saving is (I believe it would be around .2-1W) but it only makes sense I am using less power.

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I would not worry about the speed of the laptop (cpu wise) that much - I honestly do not see the point as mine is always in CPU savor mode. If I need to do rendering or editing, I do that one my desktop. The problem with a laptop will then involve using the battery more (causing more cycles on it), heating the laptop so much where it can not cool off properly, which then can lead to prematurely (unexpected HDD failure), etc.

I would suggest to just save some money on a laptop and get a desktop as they are just more reliable when it comes to the actual major processing.

PS: I can get about 6-8 good hours out of my laptop like this. And my 12cell battery is almost a year old. When the battery was new, I could do 10-12 ACTUAL hours of use..

Thanks for the thoughtful response. However I specifically stated for the sake of narrowing discussion that 'all other things are equal.' so what I'm saying is when comparing two identical laptops except for a difference in cpu, under 'average' usage (mostly email and Web browsing) would a quad-core cpu with Max 35W TDP get a lot better battery life than a dual core with 17W max TDP where the performance of each core is about the same. Essentially I want lots of battery when browsing on battery buy I want twic S powerful of a cpu when doing more intensive stuff while plugged into AC power. In that respect, seems the quad core is much more versatile.

The quad core is very likely to get less of a battery life as it has the ability to to use more power. This is fine on the charger, but like you pointed out - one can use 17W, and the other can use 35W.

To make more sense, my 12 cell battery new held about 108Wh, almost a year later, fully charged it holds about 85Wh. But like I said, my usage at 15W (total) will get me (85/15 = 5.6 hours).

If you get the laptop that can use 20W more, sure it will get the job done faster with applications, but if you figure 35W + 8-10W for other things = ~45W (100/45 = 2.2 hours). Or 17W + 10W = 27W (100/27 = 3.7 Hours).

Hopefully that made sense above. I know you asked for longer battery life and I am trying to help you achieve that, either route you go.

I am sure other people have different needs then me, but i7 laptops are usually a hefty chunk more ($ wise) than say the i3/i5. I personally would go more with an i3 (uses less power in most cases) but then build a desktop.

Other things I forgot to mention:
1) Any newer applications can take advantage of all of your threads. Maybe not 16+ threads, but typically yes. Most phone apps can even take advantage of quad+ cores now.

2) Intel will actually lock cores on some of their laptops. This may seem weird, but it helps with i7 processors with 8 threads to keep running cooler and use less power. You may actually be able to download the program and it can lock/unlock cores in some laptops which may let you get the more powerful laptop but only use say 2/4 threads when you not video editing, etc.

3) Some of those video editing programs or rendering programs can actually let you take advantage of some integrated/dedicated video cards on desktops and laptops. So you may want to look into that (see what is compatible with your program too) before buying the laptop.

You make two good points I was going to bring up. If the higher performance processor uses more battery but completes the task in less time, it can be close to "a wash" as far as how much processing/tasks you can accomplish under one charge comparing the two CPU's.

The more important point you make is that the CPU doesn't take up all the power. I say for the sake of comparison that "all other things are equal". But the question then becomes, what percentage of the total power consumption is the CPU and what percentage is everything else. So a CPU that is twice more energy efficient isn't going to get you twice the batter life. If we assumped the CPU was half the total power consumption, then it's just going to get you 25% better battery life, all other things being equal.

I've got right now a Samsung NP600B5B that has an i5-2520 and a 66wH battery. Under normal use (when the battery is newer) I get close to 4 hours.

I'm looking at an Asus Zenbook with an i7-3612QM with a 77wH battery ($899 refurb - not bad for a $2K retail ultrabook). I would expect to get significantly better battery life under "normal" non-CPU intensive use (e-mail, web browsing) I don't need Macbook battery that lasts all day.

I'm also looking at a new Lenovo Z50 (on sale $739 with Nvidia GPU) that is an i7-4510u which is only marginally faster than my i5-2520M but it's only 15W TDP. But it only comes with a 4 cell battery so battery life will be not much better than the above. I'm waiting for a response back from Lenovo as to if they have a 6-cell I can pop in on this new model.

My gut is telling me neither solution is going to be that big a difference for must of my usage than my Samsung (which is 1600x900 display, eSata, USB 3.0, etc. pretty advanced for a 2-yr old laptop). I'm probably better off just getting a new battery for my Samsung and wait for the newer Haswell models to come down in price more. I can't even find any laptops yet with the new i7-4650 which has a 278 Passmark/TDB ratio - near the top.

Like most electronics, I would say the screen uses the most power but I am not sure with laptops as much. I would say LCD/CPU probably consume 40%+ each.

The performance will probably be close to washing out, but it will probably come down to which uses less power when idle/downclocked - or if you can lock cores with either.

Rather then asking some customer support, I would use ebay. Sellers on ebay will have something for [about] everything. If your looking for a battery for a "z50" then your out of luck. If your looking for a "z500" then it looks like you can buy replacement batteries, but not really upgrade - But you will probably have to disassemble your laptop to replace.

"it will probably come down to which uses less power when idle/downclocked - or if you can lock cores with either"

This is the key reason why I'm eyeballing a quad core laptop. It would seem I could set the power profile when on battery to throttle back the CPU in order to get a quad core 35W TDP to act closer to a 15-20W CPU and thereby get siginifcant better battery life and still get the same performance as my Sandy Bridge i5. But when plugges in I could put CPU at full performance.

Could you elborate on why I'm out of luck as far as a bigger battery for the Z50? This model is so new, there's not a single review on the net so I'm wondering is the case:

a) The model uses the same battery as some other models, but Lenovo as not listed the compatible higher cell batteries yet because the model just came out, or

b) This new model uses a battery compartment that isn't compatible with any of the older models and they haven't even made a compatible higher cell battery for it yet.

I suppose another option is to get the i7-4510u and moderately overlock it to get performance somewhere inbetween my i5 and the i7 quad - but that definitely would require a better battery.

consultant said:

Could you elborate on why I'm out of luck as far as a bigger battery for the Z50?

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At least from my experience, there are usually some sort of replacement batteries on ebay. Since I do not see any, I assume the laptop is too new but also has the battery built-into the laptop. This the physical size can not be changed. At least this is what I assume.

I've owned about 11 laptops over the past 20 years, all brands and types. I've never ever seen a laptop with a non-removable battery. Does these exist, currently? Example?

Lenovo's response:

I'm very sorry, but we do not currently offer a more powerful battery for the Z50. Keep an eye on our newsletter to be informed the moment it becomes available!

My guess is it's just too new.

consultant said:

I've owned about 11 laptops over the past 20 years, all brands and types. I've never ever seen a laptop with a non-removable battery. Does these exist, currently? Example?

Lenovo's response:

I'm very sorry, but we do not currently offer a more powerful battery for the Z50. Keep an eye on our newsletter to be informed the moment it becomes available!

My guess is it's just too new.

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Mainly the ultra-thin netbooks. Like Macbooks or tablets for the mannor. Yes the battery could be removed, but not readily without opening the whole chassis.