18v vs 12v battery question
If you use a switching voltage regulator you will give you about 40% longer battery life.

A linear regulator will not. 30% of the battery energy will be wasted (LEDs may be brighter). 

   



How much you extend the battery life depends upon the voltage and current draw.
When the battery is fully charged the efficiency is nearly 90% for the chip used in this example circuit. It is important to use a regulator that is tuned to your requirements for maximum efficiency.