Intermittent "Change the Batteries" message. comes and goes but works in certain modes.

We have a Power Shot S2 IS, purchased in 05. Lately the rechargable batteries aren't working.
When turned on in shooting mode we get a black screen with "Change the batteries". If we turn it to play back mode it shows the pictures on the chip. We purchased new rechargable batteries, charged them and put them in... same thing. I put the old batteries in, and the camera worked. Put the new ones in and it worked. Removed and replaced the batteries and it didn't work - "Change the batteries" message came up again. Could this have something to do with the watch battery I read about early. Where is that?

The batteries will die after a while, lithium ion batteries begin to lose capacity and after a few years, even fully charged they don't have enough capacity to run the camera. So it's not surprising.

But with the new batteries, you should try resetting the camera, uploading the latest firmware, and cleaning your battery contacts. But after 4 years, it may just be that the camera needs servicing. However, I hate to tell you that the cost to repair the camera may be more than the camera is really worth. Rule of thumb is that if the camera repair runs north of 50% of what you paid for it, you're better off just getting a newer camera.