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My laptop is capable of running most games on high settings at decent frame rates. However, if the power cable gets unplugged while I'm playing, the game immediately starts slowing down, even if I'm using the High Performance power plan.
Why does this happen? Is the battery not able to keep up with the power demands of the GPU? Is there any way to fix this?
Egghead99
Posted 2014-12-21T20:53:13.937
Reputation: 1 565
188
High-performance mobile GPUs can require significant amounts of power to operate at full speed. The GTX 765M requires 75 W, while top-of-the-line mobile GPUs like the GTX 780M and GTX 980M can consume up to 122 W.
The GPU is not the only power-hungry part in a laptop. A modern Intel performance mobile CPU typically draws about 47 W at full power. In addition, you need to power other system components, such as the display, disk, and USB peripherals. When you add it all up, you might need anywhere from 140 W to 200 W to operate a gaming laptop under full load depending on your system configuration.
A typical battery in a gaming laptop can store about 60-80 Wh of energy. Most Li-ion batteries are not designed to be discharged faster than twice their Wh rating per hour (2C). In addition, sustained discharge at rates exceeding 1C can significantly reduce the overall service life of the battery. Continuously pulling 150 W or more from a typical 77 Wh battery is not a great idea and your battery could overheat and fail or even catch fire. While it's likely the battery's own protection circuitry would shut down the battery if overloaded or overheated, a device should never subject its battery to an unsafe load at any time during operation.
To avoid overloading the battery, the GPU will typically throttle to a lower clock speed. The GTX 780M on my personal laptop will not run faster than about 400 Mhz when on battery. Lower clock speeds reduce power consumption not only by having transistors switch less rapidly, but also by allowing lower core voltages—power consumption and heat dissipation scale with the square of voltage.
bwDraco
Posted 2014-12-21T20:53:13.937
Reputation: 41 701
20This answer absolutely needs more up-votes. It best explains why a performance laptop can't perform to 100% on batteries, even when all settings are adjusted to max performance. Incidentally has anyone ever wondered why they sell different WATTAGE power packs for the exact same laptop model? – misha256 – 2014-12-23T04:15:47.897
6Wouldn't it deserve a big bold warning if the laptop couldn't run all of its features on battery? If feel it'd be weird for this to be true with no warning from the manufacturer. Or is there one that people don't read? – user541686 – 2014-12-23T09:13:09.333
7@Mehrdad Presumably because the average consumer doesn't notice (or even care about) the reduced performance while power users know it to be an inherent limitation performance laptops. Even if it could run safely, you'd likely discharge the battery in half an hour so the use case doesn't even exist. – Lilienthal – 2014-12-23T10:20:20.627
2@DragonLord Thanks for the information. Just curious, how does the GPU know to lower it's clock speeds as to not overload the battery? – RJSmith92 – 2014-12-24T00:07:54.700
1@misha256 You get 2 or 3 of the following: 1) the cheap battery pack that's partially fully of air. 2) The normal battery pack that fills the standard size enclosure. 3) The oversize battery pack that extends outside the normal limits by either bulging out below or behind the main body of the laptop. – Dan is Fiddling by Firelight – 2014-12-24T04:36:25.950
4@RJSmith92: The BIOS basically tells the card that the system is on battery and the GPU (more accurately, the VBIOS) adjusts accordingly. – bwDraco – 2014-12-24T20:49:50.687
@DragonLord ahh right, thanks for the answer. – RJSmith92 – 2014-12-25T01:00:49.960
Any references for this? – Jason – 2014-12-26T07:20:44.187
@Jason: If you understand the limitations of Li-ion batteries and the power requirements of gaming laptops, it's not hard to come to this conclusion. I didn't consult any references while writing this answer, but these forum threads confirm it: http://rog.asus.com/forum/showthread.php?23135-G75VW-FPS-Issues-on-battery, http://rog.asus.com/forum/showthread.php?20580-G75v-Gpu-down-throttle-on-battery-(Nvidia-660m)
– bwDraco – 2014-12-26T15:07:38.303Quoting Zygomorphic on the second linked thread (emphasis original): "The 560M GPU is a 75 Watt TDP (Thermal Design Power) GPU. This would be very high power consumption on battery, especially when coupled with the 45 Watt TDP CPU. Combined load would be somehing like 110-120 Watts, which is about ten amps from a 12 Volt battery. I highly doubt that the G75VW battery can source that much current, so the throttling is necessary. Why would you want to game for 30 minutes on battery anyway?" – bwDraco – 2014-12-26T15:11:29.657
Minor correction: Actually with lower clock speed the transistors do not switch slower, they switch less frequently. The speed at which an individual transistor switches is unrelated to the clock speed. But still, great answer, got my upvote. – Christian Hujer – 2014-12-27T06:40:58.203
Paradoxically, turning settings up actually makes things slower because it wastes more of the power budget on things other than what is actually needed. The system will already use the available power budget on whatever needs it most while it's running. Forcing things to higher speeds reduces the remaining power for dynamic management. – David Schwartz – 2016-10-14T03:12:07.640
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Most graphics cards (and even integrated cards) will have a graphics control panel (Catalyst, Intel, etc) - open the graphics control panel and dig around for power-related options. I know I've seen such things myself in both Intel and AMD panels.
techniponi
Posted 2014-12-21T20:53:13.937
Reputation: 316
16
Pretty simple—because the battery can't provide enough power, so the GPU and CPU will run at lower clock speeds. Sadly, there's nothing you can do about it.
I had a laptop with a GeForce GT 540M GPU and I could play games unplugged without any problems. However, when I later upgraded to a laptop with a GT 650M, I couldn't play anything while unplugged—the GPU clock speed was just too low.
MustSeeMelons
Posted 2014-12-21T20:53:13.937
Reputation: 261
10
Most Windows laptops have quite a few more options than just power saver, balanced and high performance.
In Windows 7 and later, you can access the "advanced" power options, and it would present you with a list of all the various components in the laptop and how much power they should get while plugged in as opposed to while on battery. I think you will find that even high performance mode makes some sacrifices to spare the battery, and unless you have a truly amazing battery that is probably a good thing. You'll probably mostly want to adjust the CPU, maybe the hard drive.
doby162
Posted 2014-12-21T20:53:13.937
Reputation: 109
I've tweaked every Windows 7 advanced power option to be on max performance, and my laptop still has noticeably degraded performance while on battery. I think @DragonLord's answer is more informative. – Luke – 2015-06-10T17:33:02.523
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The battery cannot provide enough power for your laptop at full performance given that it is probably a Li-ion battery. If this is really a major problem for you, you may want to consider a Li-po battery (lithium polymer), as they are designed to have a higher output current, but it may not run for as long as a Li-ion. Here is a link for some Li-po laptop batteries.
Good luck on your future endeavors!
Nilpmet
Posted 2014-12-21T20:53:13.937
Reputation: 21
7Maybe there is something about battery power saving in the graphics drivers settings (independently from the system power mode). And the "high performance" settings on battery are not necessarily equivalent to those for external power, you can check on the advanced power properties. But it's just a guess. – Ale – 2014-12-21T21:05:28.857
1@Ale: I'm afraid this is really a hardware limitation whose absence could in fact be dangerous (as in the laptop potentially catching fire). See my answer to understand why. – bwDraco – 2014-12-23T04:35:46.297
If you have an NVIDIA GPU, try the NVIDIA PowerMizer Manager. – user541686 – 2014-12-23T09:14:57.390
1@DragonLord nice answer, very informative! – Ale – 2014-12-23T10:50:29.870
Which OS and HW specs? – Ciro Santilli 新疆改造中心法轮功六四事件 – 2018-06-09T13:32:12.220