Currently Being ModeratedFeb 12, 2013 8:10 AM (in response to _Olivier)
I'm sorry, but Apple does not provide a downgrade path for iOS. Because downgrading is unsupported by Apple we cannot discuss it on these forums, but you can use Google to find information on how to install an older version of iOS on any iDevice.
Currently Being ModeratedFeb 12, 2013 8:11 AM (in response to _Olivier)
No, you cannot downgrade iOS once it has been upgraded. If you have a problem with battery drain there are solutions that have been posted in these forums; use the Search function on this page.