4.5 V are (or used to be) pretty common in Europe for those kind of flashlights. I have a Bundeswehr one from the 70s that uses them as well. They look like this:(Image removed from quote.)Just a big, heavy block.
You can find adapters that allow the use of 3AA batteries instead of one like this (actually I think that's how they are constructed). Search for 3LR12 AA adapter and you should find several references.
They are quite common here as they were also sold to civilians (and still are, check this out: https://www.bauundhobby.ch/wohnen-licht/haushaltsbedarf/taschenlampen/militaertaschenlampe-led/p/4425412 )