And maybe to power the display? Just a guess
Uh...is there a battery inside? It may be gonzo...
IIRC, the batteries are only used to measure resistance.
Tom...Denny's been around awhile...he's remembering the classic "Simpson" multimeter and others like it. They can measure voltage/amperage without any power at all as they use an analog meter; but they need a battery to measure resistance.
As for me I'm "only" 48, but I work in the electronics industry, so I'm familiar with them -- in a nostalgic way.