Hi ciaconne,
As the most (all ?) Ixus series cameras, the Ixus 100 / SD780 don't have a removeable backup battery.
There's an internal, not removable backup battery, charged from the battery pack; it "holds" the settings for about 3-4 weeks after the battery pack has been removed.
The "Reset All..." feature on the SD780 do not reset the following setting:
date/time,
language setting,
video system PAL/NTSC,
time zone / DST setting,
the image registered as start-up image,
the saved data for custom white balance,
the colors that were selected in "Color Accent" or "Color Swap"
...and also data stored in ROM like the last errors list, the image counter...
You can change (reset) the self-registered images & sounds (like the start-up image) with the Canon software (ZoomBrowser EX / ImageBrowser), on many cameras you can also set / reset the "owner name".
