4 18650s in series is 14.4 volt. 8 1.5 AA in series is 12 volt, or 10 1.2 volt NiMH AA in series, that's also 12 volts.

Using modern LEDs with a step down setup, 14.4 volts is enough to power 3 Cree XP-Gs for 900+ lumens.

Here's an example of a 14.4 volt 18650 li-ion. 13 ounces.



http://www.batteryspace.com/customiz...fuelgauge.aspx