Low-battery alarm flashes an LED or sounds an alert when battery voltage drops below a predetermined level and (optionally) disconnects the load.
COMPUTERCRAFT Apr 1992 (v.2#4) pg. 61
Car battery and alternator monitor circuit (a simple voltage comparator). A green LED lights if your alternator is working properly. A red LED comes on if the alternator malfunctions and the battery is being drained. Est. cost: $5 (kit).
ELECTRONICS HOBBYISTS HANDBOOK 1991 pg. 63
Build a solar-charge controller, a simple comparator circuit that connects a solar panel to a battery when it senses that the battery voltage is getting low. Includes information on using several 6-volt or 12-volt batteries as part of a solar-charged electrical system.
ELECTRONICS NOW Oct 1997 (v.68#10) pg. 59
Added Info ELECTRONICS NOW Jun 1998 (v.69#6) pg. 12
Low-battery indicator circuit for a battery-operated radio which does not require a separate power supply.
ELECTRONICS NOW Jul 1998 (v.69#7) pg. 8
Circuit to monitor the condition of a battery has a red and green LED. The red LED lights when the battery voltage is low.
ELECTRONICS NOW Jul 1998 (v.69#7) pg. 8
Simple circuit lets you know when your radio-control receiver battery (or another battery) falls below a particular voltage. The alarm voltage can be preset in the range 4.3- to 10.7-volts.
MODEL BOATS #535 Sep 1995 (v.45) pg. 34
Car-battery voltage checker circuit is small enough to be installed in your dashboard.
POPULAR ELECTRONICS [2] May 1991 (v.8#5) pg. 23
Voltage indicator is used to monitor the status of any 12-volt battery. Displays results on LED's.
POPULAR ELECTRONICS [2] Jul 1994 (v.11#7) pg. 25
Using digital panel meters to enhance the look and performance of your next project. Circuits include: (1) AC power supply, (2) DC-to-DC supply, (3) DC ammeter, (4) automobile voltage monitor, (5) digital DC voltmeter, and (6) low-ohms meter.
POPULAR ELECTRONICS [2] Oct 1996 (v.13#10) pg. 39
Correction POPULAR ELECTRONICS [2] Jan 1997 (v.14#1) pg. 6
Ten-segment LED display circuit visibly indicates an automobile battery voltage over a 10.5-volt to 15-volt range.
POPULAR ELECTRONICS [2] Apr 1998 (v.15#4) pg. 55
Correction POPULAR ELECTRONICS [2] Jul 1998 (v.15#7) pg. 16
Correction POPULAR ELECTRONICS [2] Aug 1998 (v.15#8) pg. 52