Two Transistors Lead Acid Battery Monitor
Three separated LEDs is used on this battery monitor circuit. For red LED, it’s turn on from 6v to below 11v and turns off above 11v. For the orange LED, its illuminate between 11v and 13v and turns off above 13v. The green LED illuminates above 13v.
This battery indication is suitable for monitoring your car battery condition. Green indicate a good, orange is acceptable, and red is a problem of your battery. Giving early warning is the best way to keep your battery healthy, prolong its lifetime. [Source: talkingelectronics.com]