JB battery drain - better rom?

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http://forum.xda-developers.com – Hi all My wife's unbranded S2 was recently upgraded to JB but the rom is not so good as was the ICS one. Could you please recommend me good kernel or rom + kernel which is good on the battery life? Does the s2 needs to be rooted and have a custom recovery to flash another kernel etc. - I never worked with Samsung so I am not sure... Thanks for any advice! Sent from my Nexus 7 using Tapatalk HD (HowTos)