A 9 Volt Battery Checker
by Bill Hutchinson, KMSP-TV, Minneapolis
Here's a neat circuit that I put together for our remote trucks. It's a 9 volt battery checker that's completely self contained in a Radio Shack project box, with a large head screw terminal for the negative, and a smaller screw head for the positive.
Touch the battery to the heads, and the 2 color LED will be green if it's good, red if it's bad, nothing if it's really bad. Cutoff voltage between green and red is approx 7.5 volts.
It's a modification of a circuit I saw in "Electronics Now" a few months back. Hope you like it.
...... www.oldradio.com/current/9volt.htm - Oldradio.com, the Broadcast Archive