Why did so many early / cheap calculators use 9V batteries?

[Maximilian Hohmann]

Hello,

my guess would be that it is just for small size and low weight that manufacturers chose 9V batteries. Also I remember that in the 1970ies 9V batteries used to be cheaper then the alternative of 3 to 5 AA (alkaline) cells.

None of the older calculators (like Ti Datamath, Aristo M27, HP-35, Bowmar brain, Canon Pocketronic...) in my collection uses a 9V battery. They all have either AA batteries (4 or 5 of them) or a rechargeable pack.

Regards
Max