In a type 110 camera of the pocket type from a major german brand, but made in Japan, I found a battery I never came across in my many cameras:

4.5V type K

I even do not remember to have come across this battery, in a shop back then. The seller was a major post-order company, so obtaining a spare battery via mail should not have been irritant to the buyer.
Bu still, why got a general consumer camera such a battery?