I think I fried my low power circuit when I was modding the box the last time. I need to rebuild it. Since I was pressed for space I wired it freestyle so I can't easily replace components in it. I found the circuit on the net here: http://www.techlib.com/electronics/flasher.html The low battery indicator circuit. I just used a small variable resistor in series with a 470k resistor for one of the 1Meg ones so I was able to adjust the actual voltage it starts flashing at.

I am going to get the parts I need for that today and will rebuild it so I can draw up a schematic then. I will post that on my site tonight. I can run mine when the charger is plugged in. But because I am only using 5 AA cells it means I am supplying power through the charging circuit which is current limited to only supply around 90mA. That should be enough though for small things. If I had used 6 cells instead of 5 I could have made it better using a diode so I could effectively supply the 5 volt regulator part and charge the batteries without the limit but because I only have 6 volts to play with fomr the battery the 0.7 volts dropped across the diode means the voltage is too low for my regulator. You can use a 7805 but then you need your inout voltage to be 2 or 3 volts higher than your output. I can't remember the exact amount. The low drop out regulators shouldn't be hard to find though. The one I used is a LM2940CT-5. With that you only need 5.5 -6 volt input to have it regulate to 5 volts on the output.