Why 9-volt batteries?
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
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