I just performed the battery reset as described on this webpage:
http://www.pinoyhack.com/2006/09/14/...shot-s400-fix/
The battery is an SII MS614S. The battery details are here:
http://www.siimp.co.jp/product/detail_e001.html
I took the battery to a watch repair shop in hopes of finding a replacement. The store didn't have the battery, but tested it for me. The battery registered good at 3V.
I put the battery back in. Hopefully no more lost pictures for awhile...
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Tools needed:
1. #0 Philips head screwdriver, used to remove all the screws
2. 1.4 mm flathead screwdriver, used to pop the battery out
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Dismantling the camera required removing the 11 visible screws on the casing. (One of the screws is a bit hidden behind the USB port rubber cover.) Yes, it seems like you have to remove all 11 screws. Keep track of the locations since the screws are of varying lengths. I did this by drawing a rough diagram and placing the screws on it as I removed them. I would suggest start by removing the four screws for the memory card slot door. The door is spring loaded, so remove slowly and note how the spring is set in its place. There's a hairline slot for the tail end of the spring. Once all the screws have been removed, it's quite easy to pop the front and back off the camera. (You do not need to force pry it open!!) Locate the battery and pop it out with the 1.4 mm flathead. Replace it or put it back in a few minutes later.
When reassembling the camera, the front face slides in place first, straight in. The back goes in next, with the right side (camera front faces away from you) pivoting in first. Make sure the View/Shoot mode switch is on the proper side, either View or Shoot, depending on its original state when you took the camera apart. Afterward, the memory card slot cover is closed.
Upon turning back on the camera, you'll have to set the date, time and date format. All the other setting appear to have been saved, including which image number you're on.
Good luck!