I did my own sort of battery test yesterday using the latest intel generic driver. Well for starters I the power profile I put it on was a custom one I made based on a website I seen. ive tested it before on win 8 and it works well. its far more aggressive than the power savings one built in. I call this profile I made Battery Max. I took my pro off the charger at 100% charge and put it on battery max profile. my brightness was on the lower side. you would normally think I would use the pro in a fashion to stretch out the battery life but I used it as I normally would with any other power profile. I really put it through the paces using IE11 in desktop. The whole entire time I had no less than 5-8 or more tabs open at once. then I had mail app and others running in the background. I also listened to music, through pro speakers, in the background using xbox music app. So I was doing tons of web surfing, watching videos, flipping back through mail app, and such while having music playing in the background. I believe having so many tabs open contributed to the most drain on the battery as more resources are being or more ram has to be used.
I will add I never experienced any slowdown or anything as this profile I created prevents the cpu from turbo boosting. most of the time its running at about 800mHz. still amazes me how doing everyday tasks take no performance hit although im running at much lower speeds. web pages still loaded up fast and videos still played just as well. no hit on multitasking at all.
I ran this way with heavy usage on my pro on my battery max profile until my battery hit 7% left. I ended up getting a lil over 5 hours of use. remember this is with the latest intel generic driver that's not optimized for pro like the MS custom one. Now ive pulled over 6 hours before on this profile but if I remember correctly, I never had as many tabs open. So im sure I could've pulled 6 hours or so if I wouldn't of had so many things running in background and not have so many tabs open at once in IE11.
after that I rolled my driver back to latest MS custom one. probably later today or so I will rerun my usage test to see how much better batterylife I get with MS own custom Intel driver. as an engineer had mentioned it contains optimizations specific to surface pro to optimize battery life and bus speed.
so I think my pro did pretty well considering the amount of tabs I had open up at once and the nonstop usage. this was with wifi and bt on. I will post results again on the latest MS custom drivers that comes with our latest update.