I am using a 12v 5000mAh NiMH battery to provide back-up power to a circuit. The circuit draws about 500mA. To prevent damage to the battery, I need to disconnect the circuit when the voltage gets to the 10-11 volt range. I have seen a device that would work but it is relatively expensive when compared to the circuit I am powering. The Sun Saver Solar controller from MorningStar would work because it disconnects the load at 11.5v. Is there a simple, low power solution that I can build myself?