First post here so I hope I don't f#@% up.
I know there've been a million threads closed about this because everyone's setup and usage is different. I found it really frustrating to not get an 'answer', thinking to myself ‘why not compare apples with apples?’ ie stock vs custom ROM with the same usage. So I thought I'd share my experience for anyone else frustrated with the lack of “The Answer”
I bought a refurbished (new screen, battery and back cover) SGS2 GT-I9100 unlocked with Vodafone stock ROM. I was getting the battery warning at 4 hours (!) after a few calls and texts, about 15 min of FB, same for Gmail (WiFi on/Data off at home), and about an hour of driving with Google Navigation and playing music (Wifi/Data/GPS on). Battery usage showed that next to the screen at #1, GPS/Navigation was the biggest drain followed by playing music. All the other stuff was insignificant by comparison.
By uninstalling and disabling everything Samsung, Vodafone, and stuff I didn’t use, it stretched to 6 hours. 50% improvement but still unacceptable as I wanted to get at least a work-day plus travel ie 10 hours.
So a custom ROM was required which started the saga of rooting. Did hours of research and unsuccessfully tried a few through a Samsung developers’ program (Odin?). I finally resorted to spending money and sent the IMEI# to online services. Some said the phone was rootable, some not. I paid my twenty-five bucks to 1-ClickRoot and it didn’t work (but I used it to root my wife’s Motorola Mileston2) and finally rooted the SGS2 with Framaroot (I think it was either free or the price of a can of Coke). Couldn’t have been simpler – downloaded the file with the browser, explored to the (apk?) file and opened it, tried the first 2 vulnerability options unsuccessfully and on the third, success. Rebooted – voila.
I tried a few custom ROMs that, while they were highly recommended and had all the customisable bells and whistles and ‘great battery life’, I didn’t like the UI. Plus I just wanted a ‘normal’ phone with a good camera (I’m a hobby photographer) which could also browse the web, use GPS navigation, play music, have custom ringtones and pics for contacts, and the ‘important’ stuff for me at the bottom of the home screens - phone, messaging, contacts, browser and apps. I didn’t need to be able to customise virtually everything on the phone and some of these ROMs were 400-900MB compared to under 200MB for most.
Which brings me to CyanogenMod 10.1 (CM10.1). The UI is closer to standard (plus many more options) so I found the transition from the stock ROM easy. And with the same usage PLUS an EXTRA hour of Google Navigation/GPS/music – 10 hours easy with 20-33% battery left (!). Added a high capacity battery (2600mAh over 1800mAh factory, same physical size) and I now go from 0700 to 0100 the following day regularly – 18 hours with 1-9% battery left.
Hope this helps…