I bought my S2IS just after they came out, i was looking for a camera that has good video, good zoom, and Fast ! oh and an underwater housing at a reasonable price. The S2 had it all, except for the housing which i hoped would come out a bit latter from canon but never did. The previous version of this camera did have one from canon.
Any ho I digress, as time passed the camera stared behaving strangely, you would put fresh batteries in and it would say change the batteries. Then after a bit of tinkering it would work. This got worse over time, i tried different batteries and cleaning the contacts, nothing helped. Finaly about a year ago it wouldn't work at all just display that message. By that time i got 2 other digital cameras so i wasn't to stressed about it and just put the camera away. But i really missed my S2IS it shot great pics, and was handy and small (compared to my DSLR) So today i decided to finally google the question. And low and behold ! seems tons of people have had this freaky problem. So its a manufacturing problem. But what is the solution ? well all i could find is one guy saying some thing about reseting the date. So i did a factory restore to the camera (it works when connected to a power adapter just fine). And now it works ! with the same set of batteries that it didn't just before :)
I hope it will keep working. If not ill update this post.
Well the camera kept working sorta ... after a few hours i tried turning it on again, and it gave the message, but after a couple of more tries it worked. By the way i installed CHDK which is great fun and gives you an accurate reading of your battery, well it said the battries i had in the camera were at 90% full.