How much battery life does Nvidia Optimus save?

I hear it's able to switch your dedicated graphics to integrated graphics during non-heavy tasks and vice-versa during heavy tasks such as 3D games. But I want to know how much of a power saving this really is, numbers would be nice. I also want to ask when companies advertise their battery life is that with the discrete or integrated graphics on? cause that would be important i would assume.

 

Lol advertised battery runtimes are like car fuel consumption. Absolute best case scenario barely relevant to normal use patterns.

But for my experience I replaced a P150HM which would get 2.5hrs tops from new with a P170EM (similar hardware 45W tdp CPU/75+W GPU but with optimus) which would get 4 ish hrs and that was nearly a year old battery as I bought it second hand. But its hard to say how much is due only to optimus as both throttle differently on battery (P170EM down to 1.2ghz CPU...), 15.6 vs 17.3 inch screens, etc

Optimus has really fallen out of favour anyway, very few laptops with proper GPUs have the ability to use it these days, as its either optimus or gsync and the few around where you can select which you want need a reboot to swap

In more concrete numbers, which are hard to obtain, by my estimate an idling top end dGPU adds about 10-15W. How much that matters depends on the rest of the system but you can get an idea from notebookcheck's consumption data on a particular system. E.g. On something drawing an average of 30W at idle, a 10W dGPU would cut runtime by 1/4. On something drawing only 10W, another 10W would cut it in half.

 

Ooo, thinks for the insights. I have my sights set on a laptop with a gtx 940mx which boasts 12 hour battery life, many reviews say they get around 5-9 depending on the task being performed. Never made sense to me how this was possible considering it had an i5-7200u and a dedicated GPU but now I know it's that Optimus magic that every laptop with a dedicated GPU should have honestly.

 

I used to get almost ten hours battery life on the Dell Precision M6800 with Optimus enabled. With the dGPU running I'd get about 4-5 hours. Optimus is a must for me when I'm working away from a power source.

 

ok ultraportables and U series CPUs aren't really my thing, have a look at notebookcheck for similar hardware would be your best bet (they do a number of battery tests under different loads) but my comments about gsync don't apply with that lower power stuff

940mx is kinda long in the tooth I'd go for the low power 10 series models - they should offer much better performance for similar power consumption. Or use it to bargain down an older 9 series model.