I use this in all my active instruments, and also in some outboard 9V battery powered boxes. The Indicator flashes green about once per second to remind you that your electronics are powered on. When the battery drops below 7 volts, the light turns solid red.
The Indicator draws a very tiny amount of current from the battery (just 30 microamps while the battery is good), so it won’t drain it while monitoring it.
I think it would make a fun first-time surface mount project, since only one part needs to be of the surface mount variety (the dual comparator).
Cheers
Jerry