Hello Roger, I built a battery voltage indicator, in 1998, using either an LM741 or LM 311, 8 pin chips. (Note; The 311 is completely different). I have attached the 741 circuit. Can be put on a very small veroboard. I have one mounted near my 12 volt, 7 A/H battery. I have it adjusted to ~10.5 volts to enable the "flashing green LED". ( make sure you use an accurate DMM, as the circuit is sensitive down to 0.01 volts).
HTH.
L.
ps. Any gratuities gratefully accepted.......