Single led on board "low battery" indicator

This circuit is very simple and a great help monitoring your battery. Advantages on this simple circuit:

- Very low consumption (less than 2 mA stand by and 25 mA alert).
- Starts to blink on high current drain before becoming always on.
- Weights nothing and occupies minimal space.
- Easy to assemble in any instruments panel (brings some real live to the instruments panel) or any other place.
- Visible in flight and very low cost.

I used a simple PCB and all SMD components, one important point is the use of a very bright red led, transistors are not critical, but voltage divider is, low tolerance resistors are recommended, by adjusting this divider we can select the turning on voltage, in my case I defined it for 4,6 volt it gives some margin since it starts to blink at nominal 4 cell Ni-Cad pack voltage. You can find an example in my Spirit sailplane, but this project can be used in any small plane. Here is the circuit.