The only place a 9V cell make much sense is in a circuit where the
operating current is so low that you nearly get the shelf life of the
battery. Maybe a smoke detector is close to that criteria.

I have a number of devices related to amateur astronomy that use the 9V
battery.

1. Red LED flashilight.
2. Telrad 1x finder device, also uses a LED
3. Equatorial platform driven by stepper motor

All work very well, and the lifetime of an alkaline 9V cell in these
applications is typically at least a year, sometimes far more. The
stepper motor that easily rotates a 160-pound telescope is the most
amazing one to me.

Bruce Jensen