Same thing happening here.
iphone4s 64gb switches off when taking pictures (sometimes) (often enough to be annoying!)
always with 10-40% of battery remaining
it shows flat battery animation and will NOT switch on, even if holding both buttons for 2mins+
but it turns on immediately when i connect charger, no waiting to charge
and immediately shows 10-50% of battery that i knew it had
it also did it once when playing music and then someone called me
device switched off when i pressed answer button
i am jailbroken 5.1.1
it did not happen on 5.0 jailbroken (but that was when battery was new - 4 months old!)
had device for 13 months so warranty/swap is out of the question
interesting to see raviega's un-jailbroken device doing the same (post above)
did a restore fix that?
anyone else got this problem or any info?