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There is a "fairly" simple way to make what you're looking to do. A diode blocks current in one direction but not the other, but even when current is traveling in the correct direction there is a voltage drop which is deducted from the overall voltage potential. A MOSFET or similar device will have a minimum voltage to activate, or you could use an inline logic gate to trigger the MOSFET. Long story short, when slowly descending battery voltage descends low enough that when:
Vbatt - (sum of diode forward drops) < activation voltage (MOSFET or logic gate)
the MOSFET will be turned off and your lights will turn off. Another strategy would be to use a microcontroller with an ADC to measure voltage and control the MOSFET based on readings. A very simple Microchip PIC10F220 or 10F222 could do this fairly easily. The nice thing about the PIC project is you could also put a timer on it to also just run for a certain period of time and then automatically shut off.
Edit: Could also use a voltage divider with the center to the logic gate or MOSFET. With high enough resistances the current should be negligable. To be honest, the divider would be necessary with the PIC also.
Vbatt - (sum of diode forward drops) < activation voltage (MOSFET or logic gate)
the MOSFET will be turned off and your lights will turn off. Another strategy would be to use a microcontroller with an ADC to measure voltage and control the MOSFET based on readings. A very simple Microchip PIC10F220 or 10F222 could do this fairly easily. The nice thing about the PIC project is you could also put a timer on it to also just run for a certain period of time and then automatically shut off.
Edit: Could also use a voltage divider with the center to the logic gate or MOSFET. With high enough resistances the current should be negligable. To be honest, the divider would be necessary with the PIC also.
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