The s3is is a lot less vulnerable to battery parameters (at least in my case). Maybe it's because it uses 4 cells, so the camera internal voltage convertrer works in more comfortable conditions. Higher voltage requires less current, so it's more energy efficient. Small digicams with 2 cells tend to "die" much faster, especially when taking photos with flash. This is not only because 2 cells can store less energy. Those two cams: (s3is and a570) have different current drain of course, mostly because of mechnical design and mass of moving parts. To make a comparable test, both should be tested with AFL, AEL etc. so that only the CCD sensor and the electronic circuit were consuming the current. The result (I guess) would be that i.e. a570is made 200 photos, while s3is around 500.
My suggestion to Hacki: try to make those measurements with additional 0.05...1 Ohm resistor (several within this range) conected in series with the PSU, and You'll see what happens (its better to do it without the SD card).
this "feature" will lead only to camera crahes, stops and/or filesystem corruption...
I would take that risk. If the "write" LED acts the same like a computer HDD LED, the SD card operations are always conducted in a "low" energy drain phase (in Play mode or after taking a shot). The voltage drop should be far less than when i.e. charging the flash. I agree, that this is VERY DANGEROUS, buy the User has ALWAYS the CKDK's voltage lever indicator... and should react even better than the software