I for one have never seen a battery in a printer other than for a portable
I have to admit, I've not actually "seen" a battery in a printer. But
given the fact that the average PC still uses battery backed up bios
settings, it's clearly not impossible. I know in the old days NVRAM
was used in some printers which was basicly a ram chip backed up by a
battery which was picky backed on the chip and encased in plastic and
glued on with epoxy. Eventually after years, or decades these
batteries would fail. The reccomended solution was to buy a new NVRAM
chip which were typicaly in the $20 range the last time I looked.
Alternativly one could scrap away the epoxy and get at the wires
between the piggy back, cut them and solder on a new battery pack. In
a pinch one could if they were careful short out the battery to clear
the memory. You would only do this on systems that absolutely had to
be back online as soon as possible and you couldn't wait for a
replacement.
I don't know what canon is using. I suspect it's a EEPROM.. probally
because that's what the service manual says.