Beaulieu R16 battery voltage

[nikonr10]

I have had a beaulieu R16 for many years, I always use the external battery pack which is made in Germany at 1991. it is written on the battery that it is +-4.2V
However, I discovered recently that the Beaulieu r16 takes 7.2V for the motor and 3.6v for the light meter.
It is so strange to me that how could a 4.2v battery working without any problem for a 7.2v camera for many years?

Hi you can also use's a nizo battery box with AA batterys wired up /or a 7.2v RC car battery from a model shop .
a penny for the guy !

This is the best way I found and cheap any r/c model shop ?